From the collection of the
Prefinger
i a
Uibrary
San Francisco, California 2007
JOURNAL
OF THE SOCIETY OF
MOTION PICTURE ENGINEERS
Volume XXXII January, 1939
CONTENTS
Page Undersea Cinematography E. R. F. JOHNSON 3
The Road Ahead for Television I. J. KAAR 18
Report of the Studio Lighting Committee 44
Photographic Effects in the Feature Production "Topper"
R. SEA WRIGHT AND W. V. DRAPER 60
Latent Image Theory and Its Experimental Application to Motion Picture Sound-Film Emulsion W. J. ALBERSHEIM 73
The Evaluation of Motion Picture Films by Semimicro Testing
J. E. GIBSON AND C. G. WEBER 105
Current Motion Picture Literature 110
Spring, 1939, Convention '. 113
Society Announcements 117
JOURNAL
OF THE SOCIETY OF
MOTION PICTURE ENGINEERS
SYLVAN HARRIS, EDITOR Board of Editors
J. I. CRABTREE, Chairman
A. N. GOLDSMITH L. A. JONES H. G. KNOX
A. C. HARDY E. W. KELLOGG G. E. MATTHEWS
Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, included in their annual membership dues; single copies, $1.00. A discount on subscription or single copies of 15 per cent is allowed to accredited agencies. Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. Published monthly at Easton, Pa., by the Society of Motion Picture Engineers.
Publication Office, 20th & Northampton Sts., Easton, Pa. General and Editorial Office, Hotel Pennsylvania, New York, N. Y.
West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. Entered as second class matter January 15, 1930, at the Post Office at Easton, Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of Motion Picture Engineers, Inc.
Papers appearing in this Journal may be reprinted, abstracted, or abridged provided credit is given to the Journal of the Society of Motion Picture Engineers and to the author, or authors, of the papers in question. Exact reference as to the volume, number, and page of the Journal must be given. The Society is not responsible for statements made by authors.
OFFICERS OF THE SOCIETY
** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. ** Past-President: S. K. WOLF, RKO Building, New York, N. Y. ** Executive Vice-President: N. Levinson, Burbank, Calif.
* Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. ** Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y.
* Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. ** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio.
* Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y.
* Treasurer: L. W. DAVEE, 153 Westervelt Ave., Tenafly, N. Y.
GOVERNORS
** M. C. BATSEL, Front and Market Sts., Camden, N. J.
* R. E. FARNHAM, Nela Park, Cleveland, Ohio.
* H. GRIFFIN, 90 Gold St., New York, N. Y.
* L. L. RYDER, 5451 Marathon St., Hollywood, Calif.
* A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass.
* S. A. LUKES, 6427 Sheridan Rd., Chicago, 111.
** H. G. TASKER, 14065 Valley Vista Blvd., Van Nuys, Calif.
* Term expires December 31, 1939. ** Term expires December 31, 1940.
UNDERSEA CINEMATOGRAPHY E. R. F. JOHNSON**
Summary. — The dates of the first recorded use of underwater photography and the tendencies toward its increasing use by producers are noted, and the author's early experiences in this field are described. For work in natural settings the most useful equipment consists of submergible cameras placed on the bottom and operated by divers. The problems of and equipment for such work are dealt with and it is pointed out that studio tank work shares most of these problems.
The optical properties of water are described. Since water is less transparent than air, photography by natural light is limited to shallow depths and more power is required for artificial illumination under water. Since colors are not absorbed equally, accurate monochrome rendering and photography in natural color are com- plicated. Haze limits the distance at which pictures can be taken under water, but is largely confined to a part of the spectrum and can be partially eliminated by the use of color filters. It is plane polarized and can, therefore, also be suppressed by the use of polarizing plates. The advantages of this method are briefly stated — it does not distort monochrome rendering and can be used in natural color photography.
The ideal attributes of equipment for use in underwater cinematography are outlined and available equipment is briefly described.
HISTORY AND CURRENT STATUS
The first recorded attempt to take photographs under water that has come to our attention was by Boutan in 1893 and we understand that he succeeded in securing a few fairly successful still pictures.
The possibilities of underwater motion pictures seem to have in- trigued the fancy of commercial producers almost as early, if indeed not earlier, than it did the scientists and educators. Williamson produced the underwater picture, Twenty Thousand Leagues under the Sea, in 1915-16, and at about the same time scientists, among whom were Bartsch, Beebe, and Minor, started using water-tight motion picture camera housings in conjunction with the suitless type of diving helmet, in order to take motion pictures with which to illustrate their lectures upon underwater life.
* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 3, 1938.
** Mechanical Improvements Corporation, Moorestown, N. J.
3
4 E. R. F. JOHNSON [j. s. M. P. E.
Recently the tendency of producers to show what happens under water as a part of their stories has grown vastly, to say nothing of pictures having the principal parts of their plots based on action allegedly taking place there. Indeed pictures of champion divers or swimmers are no longer considered complete without a view of their graceful evolutions after penetrating the surface. Some real ocean water scenes were used in the excellent story Submarine DI and underwater scenes can be used to add to the romantic touch of a picture, as was done in Jungle Love. The work of naval and com- mercial divers has as yet hardly been touched upon and their heroic exploits offer material for a host of future thrillers. People in ever- increasing numbers are becoming cognizant of the real underwater conditions. For instance, Miami University has a class in marine zoology where the students, using diving helmets, go below the sur- face. At the Marine Studios in Florida and at the Bermuda Aquarium tourists put on diving helmets, or observe the underwater world through ports. In France, Paul Painleve's underwater club is edu- cating another section of the public. This increasing familiarity is making audiences more critical, and the technic and equipment for actual underwater photography as contrasted to shots through glass port-holes in tanks are of both present and growing importance to entertainment pictures, as well as to the scientist and educator.
PHOTOGRAPHIC CONDITIONS UNDER WATER
The author's vigorous attack on the problems involved in under- water photography was brought about by a stinging defeat in 1928. We read one of Beebe's glorious descriptions of the beauties of under- sea gardens and the complete ease with which they could be visited and photographed. An Eyemo camera was enclosed in a simple case with a box of calcium chloride to keep the condensation off the lens and window. The result of several weeks' work was very mediocre, however, for we found out that if one can see forty feet that does not mean that he can take good pictures at more than ten, or always even up to ten. We found that natural light is strong enough for photography under water only between 10 : 30 A.M. and 3 : 30 P.M. in the summer and even less in winter ; that the pellucid tropic seas are more often than not full of white sand, green algae, gray-green marl, or other detritus; and that if the undersea photographer hoped to get anything in a natural set he had to be lightning fast to grasp his opportunity.
Jan., 1939] UNDERSEA CINEMATOGRAPHY 5
Diving bells and baby submarines were considered, but after talking with a few persons who had had experience with such equip- ment, we saw that they could not be transported and put into position with sufficient ease and speed to suit the underwater photographer, and they are the plaything of every wave or squall of wind. We at- tached cameras to water telescopes; we shot them through glass- bottomed buckets; we submerged them and sighted through peri- scopes. But pictures from an unsteady base are unattractive and tend to make the audience seasick. It is our opinion, therefore, that underwater pictures can best be made from the bottom and not the surface ; also, that a compact underwater camera operated by a diver should be used for all picture work in the open sea, lakes, and rivers. The same applies to a considerable degree also in swimming pools and tanks, for the cameraman shooting through a port-hole is greatly hampered in following a moving object, and most underwater sub- jects depend on action rather than expression to tell their story.
The physical qualities of water are responsible for many of the difficulties encountered in underwater photography. The purest of water is far less transparent than air; and, because it is an excellent solvent, it is rarely pure in nature; and dissolved matter profoundly affects the optical properties. Then, too, water, having greater den- sity and viscosity than air, supports a much greater proportion of suspended matter both organic and inorganic, and this has an even greater effect on its optical properties. The quantity and kind of dissolved matter are relatively constant for any location and, at least in sea water, are nearly the same for almost all areas where underwater pictures can be taken. Suspended matter, on the other hand, is highly variable both for different locations and at the same location with varying season and weather. It is the quantity of suspended organisms and particles that finally determine whether or not satisfactory pictures can be taken at a particular place or time.
OPTICS OF UNDERWATER PHOTOGRAPHY
In undersea photography it is general practice to use ordinary cine lenses computed for use in air — protected by a plane window. This introduces a water-air boundary which affects the focus and correc- tions of the lens. Objects under water appear nearer and larger both to the eye and to a camera. We have computed the effect upon focus and it turns out that the ratio of the air focus to that under water is equal to the index of refraction of air with respect to water. The
6
E. R. F. JOHNSON
[J. S. M. P. E
index varies with the salinity and temperature of the water but the value 0.750 may be used for all conditions with negligible error. It follows that to focus on an object at any distance under water the same lens extension is required as for an object at three-quarters of that distance in air.
The presence of the water-air boundary in front of the lens also introduces both spherical and chromatic aberration. Fortunately, if the plane of the window is perpendicular to the axis of the lens, they are both too small to require correction. In tank work any attempt to position a camera other than normal to the plane of the window will result in objectionable aberration.
5000 6000
VIOLET Bi_ue GREEN YELLOW OKAVKE
FIG. 1. Spectral quality of mean noon sunlight at the surface, and through 25 and 50 feet of water.
When photographing by sunlight, the first factor to be considered is the overall reduction in intensity of light. This varies greatly with conditions, but it is our experience that under average conditions twenty-five to thirty-five feet is the limiting depth using rapid lenses and Eastman Super X or Agfa Supreme film and a filter with a factor of from two to four. The newer ultra-rapid films extend this limit somewhat. Fortunately the largest percentage of interesting marine life and human activity is to be found within this range. At greater depths photographic subjects become more scarce and difficulties are materially increased.
A further complication is added by the fact that water does not absorb different colors equally. Fig. 1 shows the approximate inten- sity and spectral quality of sunlight at the surface and at several depths in water. The curves were computed from the laboratory
Jan., 1939]
UNDERSEA CINEMATOGRAPHY
measurements of the transparency of sea water by E. O. Hulbert1 and approximate the conditions found in practice. It will be seen that sea water is most transparent in the blue-green region between 4400 and 5400 A and that the red is quickly absorbed. This filtering ac- tion of water makes difficult a true monochrome rendering of subjects, and has an even greater effect on photography in natural colors. In color photography compensating filters can be used to correct for the spectral quality of the light at any given depth. It is to be noted, however, that theoretically a different filter would be required for every depth. Moreover, the same would be true for different dis- tances from the camera to the object. Thus, if an object at six feet
ZS
4000
S5oo
4500 5000
WAVE LENGTH A
FIG. 2. Spectral distribution of water haze in sea water; transmission curve of Wratten Aero No. 2 filter.
from the camera and six feet deep is being photographed, a compen- sating filter correct for twelve feet of water would be required. How- ever, even though filters are used objects closer than six feet would tend to be too red and at greater than six feet would be progressively greener — the background fading out in a uniform blue-green. This, in fact, is a real effect. Objects at a distance do not appear to be the same color to a diver as when they are close by. A diver's vision fades out in a misty blue-green haze. Color-film, however, accen- tuates this effect, making the background an unnaturally intense blue-green. We have taken both Kodachrome and Duf ay color stills and Dufaycolor motion pictures, most of which exhibit this effect. By proper limitation of depth and distance, however, beautiful results can be obtained.
8 E. R. F. JOHNSON [J. S. M. P. E.
The greatest bete noire of the underwater photographer is water haze or "nuisance light." It is strictly analogous to aerial haze but being much more intense its effect shows up in the picture of an ob- ject only a few feet away rather than a matter of miles. This haze originates in the scattering of light by the water and by dissolved and suspended matter between the camera and the object. Its effect is to cause a uniform exposure over the whole picture, which tends to mask detail and contrast; as the distance becomes greater the haze becomes brighter, compared to the brightness of the object, finally masking it completely.
It was felt that water haze, like aerial haze, should consist prin- cipally of light in a limited spectral region and that a color filter would eliminate much of it. With this in mind we conducted a series of experiments with an underwater spectrograph. Fig. 2 gives the relative spectral distribution of the haze light in the sea water off the Florida Keys.2 Tank tests with distilled water gave an almost identical curve. Camera tests showed a great improve- ment when a Wratten Aero No. 2 filter was used. The transmission curve of this filter is also given. Fig. 3 shows the improvement obtained by the use of filters : (a) is a scene at a distance of six feet with no filter; (b) a similar scene using an Aero No. 2; and (c) with a Wratten No. 25 filter, which transmits only the red rays of wave- lengths greater than 6000 A. This last picture shows only very slight improvement in detail over the one taken with the Aero No. 2, and this improvement is more than offset by the unnatural appear- ance of the subjects and by the extreme exposure increase required. The chief objection to the use of color filters to eliminate haze is the fact that water is most transparent to the blue-green region of the spectrum ; but this is also the region of maximum intensity of the haze light, so in eliminating it the most efficient photographic light is also lost. Fortunately there is another means of cutting out this troublesome haze.
So far as haze light is concerned studio tank work offers the same problems as natural settings — as we believe at least one producer has found, to his sorrow, after putting several thousand gallons of expen- sive distilled water into a nicely scrubbed tank and then failing to get the clear crisp pictures he wanted so badly.
The fact that this nuisance light is present even in distilled water that has stood long enough to be free of air bubbles indicates that the origin of much of it must be molecular scattering by the water it-
Jan., 1939]
UNDERSEA CINEMATOGRAPHY
FIG. 3. Use of color filters to reduce water haze; (a) no filter. (6) Wratten Aero No. 2 .filter, (e) Wratten No. 25 filter.
10 E. R. F. JOHNSON [j. s. M. P. E.
self. Therefore, according to the Raman-Einstein-Smolchowski theory it should be almost completely plane polarized.3 Our dis- covery of this fact led to our use of polarizing screens. By the use of these screens it is possible to eliminate a greater part of the "nuisance light" than by any other means. Their use requires an exposure in- crease of from two to four times. Unfortunately, the haze light is not completely polarized, so, while the distance at which satisfactory pictures can be obtained is extended, there is still a very definite limit.
Probably the most advantageous feature of this method of elimi- nating haze light is that polarizing screens are almost perfectly spec- trally neutral. They do not distort the monochrome rendering nor do they eliminate the most useful portion of the spectrum as does a yellow or red filter. This spectral neutrality further makes possible haze elimination when using color-film. However, at present the speed of color-film does not permit the use of both a compensating filter and a polarizing plate under normal conditions. If the speed of these materials can be doubled a great improvement in the quality of undersea color pictures is anticipated by the use of polarizing screens.
Light-rays passing into water through the surface are bent until they travel nearly straight down, so by natural illumination subjects under water are inclined to be overly contrasty with highlights on top and densely shadowed undersides. We tried relieving this situation with reflector boards but found that boards large enough to help at all had so much water resistance that even in slack water they were difficult to handle and with any current it became impracticable either to set them or keep them in position. Shadows can be re- lieved to a certain extent by the use of artificial lights. Reflectors must be small and highly efficient or they become unmanageable in any current. In using lights, it is necessary to exercise extreme care in placement, otherwise haze light makes the lamp beam visible. Since most of the energy from incandescent lights is in the red end of the spectrum, in which region the water has its strongest absorption, the power requirements are much greater than for equivalent illumina- tion at the surface.
EQUIPMENT
Having outlined the technical and practical difficulties confronting the underwater cinematographer we shall now briefly describe the ideal attributes of apparatus to meet these difficulties and the prac- tical equipment developed by/our company, for this specialized field.
Jan., 1939] UNDERSEA CINEMATOGRAPHY 11
Motion picture producers early learned that dependence upon na- tural light could be extremely expensive, sometimes tying up the whole staff of actors and technicians for days waiting for favorable conditions. In underwater photography the clarity of the water and the size of the waves are also factors that can vary independently of sunlight, thus further limiting the useful part of time on location. Moreover, even under the best of conditions, the working day under sea is shorter than at the surface; first, because the sun reaches full brightness later and fades earlier; and, second, long exposure to water soon tires both cameramen and actors. These factors tend to run up the expense of underwater footage and demand a high standard of re- liability, convenience, and speed of operation in the apparatus used.
Sending equipment to the surface for adjustments of stop or focus or change of filter is wasteful of time. It is, therefore, the first re- quirement of underwater equipment that the controls for all adjust- ments be quickly and conveniently operable under sea by the diver.
The fact that water is a far less yielding medium than air dictates other requirements. A camera that would be quite stable in a twenty-mile wind might easily be thrown over by even a two-mile current. When working at small depths the under-surface surge from waves tends to sway and billow both diver and equipment. Very often the diver has difficulty in standing or walking even with- out apparatus. Therefore, tripod mount and spring or electric motor drive are essential. Apparatus must be compact to keep down its water resistance; it must be light enough for ease in carrying, yet heavy enough to be stable. All connections must be rigid.
When under water, man becomes a clumsy, slow-moving creature. It is, therefore, important that any couplings that must be made should be large and simple. Calibration markings should be large and distinct, and all controls and calibrations should be visible and operable from one position.
Even after short submergence the skin of a diver's hands becomes softened and very easily cut by things that would not do so at the sur- face. For this reason everything must be smooth with no sharp edges.
The construction of diving helmets, and the fact that the camera- man has difficulty in remaining perfectly still, make it necessary that view-finders be corrected for an eye position well back of the port, and, further, the reduced illumination makes important a large brilliant image.
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E. R. F. JOHNSON [J. S. M. p. E.
FIG. 4. Professional model underwater motion picture camera.
FIG. 5. Underwater housing for Bell & Howell Eyemo, open for loading.
Jan., 1939] UNDEkSEA ClNEMAtOGkAPfiY "13
Direct focusing is a difficult if not impossible task and therefore accurate focus calibration of lenses is a necessity.
In developing apparatus for underwater cinematography we have not undertaken the design of new camera mechanisms but rather have modified for underwater use the excellent existing surface equip- ment. The materials and construction of all apparatus are such that no condensation occurs on windows when submerged, thus eliminating the need of troublesome and time-consuming chemical driers. In general, it may be said that any surface camera can be encased for such use, but for our standard models we have selected those whose size and layout make them most adaptable for the purpose.
FIG. 6. Professional model underwater still camera.
The most complete unit is the professional model motion picture camera, Fig. 4, which was designed to give the underwater cinema- tographer an instrument possessed of the greatest possible flexibility and convenience of operation.
The camera mechanism is the Akeley, with a capacity of 200 feet of standard 35-mm. motion picture film. It is driven by an electric motor with external speed control. The trigger switch is in a sepa- rate water-tight case mounted on the cable; it may be used at a short distance from the camera or mounted on the guiding handle of the tripod, making it possible to guide and run the camera with the left hand, leaving the right hand free to adjust focus and aperture. A
14 E. R. F. JOHNSON [j. s. M. P. E.
Veeder type of footage counter is at the rear of the case, and every two feet a dim light flashes at one side of the view-finder, permitting the cameraman to keep count of footage without looking away from the scene. Three lenses, wide-angle, standard, and telephoto, are mounted in the instrument. These are in a vertical row rather than in the conventional turret, in the interest of simpler lens and filter control. Provision is made for two color niters, which may be thrown in or out at will, and a polarizing plate which may be racked in front of the lens or removed. It may also be rotated under water and a sun's position indicator on the rear of the camera indicates the proper rotation when using natural light.
The view-finder gives a large brilliant image and incorporates ad- justment for correction of parallax. Supplementary lenses are used
to obtain the fields of the dif- ferent camera lenses without a reduction in the image size.
In air the camera weighs approximately seventy-five pounds but submerged only twenty-five, which makes it an easy load for a single diver. The water-tight covers of the camera and lens compartments
FIG'7' nd™hngf°rWeS' are ga^keted and held fast by
quick-acting latches which re- quire no tools to operate and make loading an extremely rapid opera- tion. All controls are clearly calibrated and visible from the operat- ing position. The diver-cameraman can accomplish all adjustments under water with the exception, of course, of reloading.
We have also a housing for the Bell & Howell Eyemo, Fig. 5. In this case the camera is removable from the water-tight case. The only permanent alteration is the addition of fittings to the lenses which in no way interfere with the ordinary use of the camera in air. The case will accommodate any of the standard Eyemo lenses up to the 3 3/4-inch focal length. Lenses can not, however, be changed under water. Provision is made for the underwater adjustment of lens focus and aperture, for winding of the spring motor, and operation of the trigger. All controls are visible and adjustable from the rear of the camera. There is a single large case opening which is gasketed and held by quick-acting latches, and it is not necessary to remove
Jan., 1939]
UNDERSEA CINEMATOGRAPHY
15
the camera from the housing which reduces to a minimum the time required to load or change lenses and niters.
There is also available a professional model still camera, Fig. 6, which, because it uses standard 35-mm. motion picture film, can be
FIG. 8. Underwater range-finder.
used for taking check stills of motion picture scenes as well as for or- dinary still pictures. This instrument makes use of the Leica camera mechanism, and all controls can be operated by the diver more con- veniently than in the average air camera. It is necessary to take it to the surface only for film reloading. It weighs in air approximately twenty- four pounds and submerged, about ten. There is an underwater choice of no filter, either one of two color filters, a polarizing plate, or combina- tion of filter and polarizing plate. There is also provided an indicator for determining the proper degree of rotation for the polarizing plate. A large brilliant-image field-finder is in- corporated in the camera as well as a built-in range-finder coupled to the camera lens in the. interest of rapid focusing.
"For determining the correct exposure under water, which is essential as the light available varies greatly both in amount and color with, differences in depth, the amount and kind of impurities present, arid the condition of the water surface, there, is a
PIG. 9. Underwater lamp.
16 E. R. F. JOHNSON [j. s. M. P. E.
substantial water-tight housing for a Weston model 650 exposure- meter, Fig. 7.
Accurate measurement of distance is also necessary. Under most conditions illumination is relatively weak and aperture settings must be large, resulting in short focal depth. Under water the eye is a very poor judge of distance and yardstick measurements are often difficult. To make quick accurate measurements possible an underwater range- finder has been developed, Fig. 8. It is of the double-image type, different from the conventional instrument only in the increased size of the optical parts and in the calibration which gives true dis- tances under water.
FIG. 10. Amateur underwater still camera.
For supplementing natural light there are special underwater lamps (Fig. 9) using corrosion-resistant reflectors, which for ease of handling in underwater currents are of comparatively small size. Special diving lamps as well as standard photofiood lamps in water- proof sockets can be used in these reflectors.
Because of an increasing interest on the part of amateurs in this field we have designed a compact still camera (Fig. 10). It takes pictures 2x/4 X 2x/4 inches and is equipped with a rapid lens. All necessary controls can be operated under water and filters and polar- izing plate may be used. It incorporates a fitting for flash bulbs which is synchronized with the shutter. The only concession to the low price demanded of an amateur camera is a slight sacrifice in the convenience and rapidity of operation. In a short time we expect to have a similar case for one or more of the popular 16-mm. motion picture cameras.
Jan., 1939] UNDERSEA CINEMATOGRAPHY 17
REFERENCES
1 HULBURT, E. O.: "On the Penetration of Daylight into the Sea," J. Opt. Soc. Amer., XXII (July, 1932), No. 7, p. 408.
2 DARBY, H. H., JOHNSON, E. R. F., AND BARNES, G. W.: "Studies on the Absorption and Scattering of Solar Radiation by the Sea," Carnegie Inst. of Washington, Publication No. 475 (Oct. 15, 1937), p. 191.
3 RAMAN: "Molecular Diffraction of Light," Proc. Royal Soc., 101 (1922), p. 64.
DISCUSSION
MR. KELLOGG: For getting a light background, do you ever inject into the water something that will produce a milky cloud behind the subject so that it will not obscure the picture?
MR. JOHNSON : We have never attempted to do that. There is so much milki- ness in the water naturally that we have never thought about adding any. The background tends to come up and hit you in the face. You are seldom more than twenty feet away when this nuisance light or haze light obscures everything. Generally we try to get as much animal or plant life or coral growth or sand bank or other physical object in the background rather than to leave a lot of this fog.
MR. CRABTREE: Have you used artificial light?
MR. JOHNSON: Yes. The trouble with artificial light is that we have to have such a tremendous quantity of it to amount to anything. The red rays become dissipated in heat, and of course most artificial light has plenty of red rays in it.
MR. CRABTREE: Possibly the high-intensity mercury- vapor lamp would be useful. It would at least be water-cooled.
MR. JOHNSON: It would be a better lamp than some of the others. In tank work I am inclined to use a lot of artificial light, but from below rather than up above.
The light from a sodium lamp would introduce far less haze than that from a mercury lamp, but for underwater photographic use a lamp of high efficiency over a wide range of the spectrum should be selected. We therefore do not recommend either mercury-vapor or sodium lamps as especially useful to the underwater cinematographer.
MR. CRABTREE: I noticed a tripod in one of the pictures. The construction seemed to be quite different from that of the normal tripod.
MR. JOHNSON: The tripod was a specially built brass tripod, made like a slide trombone, so you could move it in and out from the standing position. It is made very solid, because under water one is pushed around a lot so he can not use a surface tripod.
THE ROAD AHEAD FOR TELEVISION* I. J. KAAR**
Summary. — Now that television standards have been agreed upon in the United States, commercial receiving sets will undoubtedly be available very soon, and regularly scheduled television programs may be expected at the same time. How good will the television be and what are the problems yet to be solved before television reaches the technical maturity that radio has today? These are questions of considerable interest to engineers in related fields, and are the subject matter of the present paper. The quality of present-day television pictures is compared with that of motion pictures both in the theater and in the home. A discussion is given of the problems that have been solved to make television what it is today, and consideration is given to the problems that must be solved to make television what we hope it will be tomorrow. The problems of signal propagation and interference are discussed, and the matter of network program distribution is considered. Finally, a short introduction is given to the commercial problems in television.
For several years the public has been increasingly curious to know when television would be introduced commercially, and a great variety of explanations have been advanced by uninformed persons as to why it has not happened already. Of course, at first the reason was lack of technical quality; but in the past few years the quality of pictures achieved has certainly been good enough to interest an increasingly large proportion of the population. However, two major questions had still to be answered before the widespread commercial introduction of television. The first of these was the fixing of satis- factory television standards and the second was the discovery of a satisfactory method of paying for the programs. The first matter has practically been settled; the second has not.
Television differs from sound broadcasting very markedly in the importance of standards. In sound broadcasting, if the method of modulation (amplitude, frequency, or phase) is once determined, any receiver which can be tuned to the carrier frequency of a given trans- mitter can receive its program. The technical quality of transmitted
* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 21, 1938.
** General Electric Company, Bridgeport, Conn.
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THE ROAD AHEAD FOR TELEVISION 19
programs can be improved year by year, but while this happens, a receiver once purchased is always usable, even though it may become outmoded as compared with current models. The situation in tele- vision is quite different. Due to the use of scanning and the necessity of synchronization between the receiver and transmitter, if trans- mission standards are changed, receivers designed for the old stand- ards become useless. Because of this fact, no responsible manufac- turer would sell receivers to the public until standards were fixed by
FIG. 1. Typical scene in British television studio.
the industry and sponsored by the Federal Communications Com- mission. Furthermore, American manufacturers did not desire to fix standards, except at such a high quality that widespread and sustained interest on the part of the public would be assured and so that adequate provision for continued perfection was possible. It required considerable technical perfection to justify these high stand- ards, but this has now been attained and the essential standards have been agreed upon. Consequently, it may be said with some assurance that the last technical obstacle in the path of commercial television has been removed, at least so far as the excellence of the picture under proper conditions is concerned.
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I. J. KAAR
[J. S. M. P. E.
The question of who shall pay for television programs has not yet been answered. As is well known, the cost of sound broadcasting is borne by "sponsors," who pay enough for their own programs to enable the stations and networks to fill-in the unsponsored time with sustaining programs of good quality and to make a profit in addition. However, this situation now requires the existence of tens of millions of receivers in the country with listeners who may be induced to buy the advertised products. Such an audience does not exist in television
FIG. 2. Typical scene in American television studio.
and can not be expected for several years. Of course, no such audience existed in the early days of sound broadcasting either, and the re- ceiver manufacturers themselves, along with a few individual com- panies who built stations for their own advertising purposes, operated the stations. In those days, however, the thought of something com- ing through the air, receivable at no cost, was an entirely new one. People were quite satisfied with the new toy as such and program excellence was a secondary consideration. This, of course, meant that the cost of broadcasting (as compared to the present) was low. Now the public has been educated to expect a high degree of excellence
Jan., 1939]
THE ROAD AHEAD FOR TELEVISION
21
in program material and it is doubtful if mediocre program material in television would be acceptable. This has been quite strikingly proved in England. In other words, when television is born, it must be born full-fledged as far as program material is concerned. This, of course, means great expense which, undoubtedly, will have to be borne by the pioneers.
In Great Britain commercial television is already a reality and it is of interest to consider some of its various aspects. American tele-
FIG. 3. An outside pick-up in England.
vision will be quite similar, except for improvements based upon the progress of the art since the British standards were set.
Fig. 1 is a photograph of a television studio showing the general layout. In particular there is seen the performer and the position of the camera tube and the microphone.
Fig. 2 is a similar set-up in an American studio.
Fig. 3 is a scene showing a camera tube being used for outside pick-up in England.
Fig. 4 is an unretouched photograph of an image on the screen of a picture tube in England.
Fig. 5 is a similar picture taken in America.
22
I. J. KAAR
[J. S. M. P. E.
FIG. 4. Photograph of picture tube image in England.
FIG. 5. Photograph of picture tube image in America.
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 23
Fig. 6 is a view of the antenna tower of the London (Alexandra Palace) Television Transmitter. The mast carries two separate aerials, vision (above) and the accompanying sound (below) .
Fig. 7 is a view of the interior of a mobile television control room in England. At the center of the photograph are the picture monitors. This equipment is mounted in a "van" and has been used very suc- cessfully at sporting events. The signals in this case are transmitted to the main transmitter at very short wavelengths and rebroadcast at high power.
Fig. 8 is a view inside an American "van" serving the same purpose.
STANDARDS
Let us next briefly consider the television standards which have been adopted in this country and the reasons for their adoption. The reader is no doubt acquainted with the general scheme of television used, but a quick review of the essentials may be in order. At both the camera tube and the picture tube, the picture is scanned by an electronic spot (beam of electrons) in a series of adjacent horizontal lines. The number of these lines into which the picture is divided in the scanning process determines the fineness of vertical detail which is reproducible. After scanning the whole picture, the elec- tronic spot then repeats the process at a sufficiently rapid rate so that no apparent flicker exists. This process is essentially the same, so far as the effect upon the eye is concerned, as that performed by the shutter on a motion picture projector. The frequency of repetition of scanning of the whole picture is known as the frame frequency.
In order to conserve ether space, it is desirable to keep the frame frequency as low as possible. Consequently, an artifice is employed in order to increase the apparent frequency of repetition. This device is known as "interlace." In an "interlaced" picture every other line of a picture is scanned, and after the whole picture has been scanned in this way, the lines in between are scanned. This gives the physiological effect of scanning the picture twice, as far as flicker is concerned, even though all details of the picture have been com- pletely scanned only once. The apparent flicker frequency under these conditions which is twice the frame frequency, is known as the field frequency. Now obviously, if anything other than a complete blur is to be obtained, it is necessary that the number of lines per frame, the order of scanning of the lines, and the number of frame_s
24
I. J. KAAR
[J. S. M. P. E.
per second be identical at the receiver and transmitter. These, ac- cordingly, have been standardized in America as follows :
Number of lines per frame = N = 441 Number of frames per second = F = 30 Number of fields per second — 60 (interlaced)
To these we may also add the standard picture aspect ratio, which is 4:3 — in agreement with the value used in motion pictures.
FIG. 6.
The Alexandra Palace television station in London.
There is a reason for choosing the number 441 rather than some other number of about the same value. It may be shown that a necessary requirement for a stable relationship between the horizontal and vertical scanning oscillators, is that the number of lines per frame be a whole number having only small odd factors. If no factors larger than 7 be used, Table I shows the list of possible values of N. Four hundred and five lines per frame is the figure chosen as standard in Great Britain, while in some very fine laboratory pictures shown in Holland, 567 lines were used.
Jan., 1939]
THE ROAD AHEAD FOR TELEVISION
25
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26 I. J. KAAR [j. s. M. P. E.
There is also a good reason for using 30 as the frame frequency. It is found that unless the frame frequency is a multiple or a sub- multiple of the power supply frequency, a shadow will move across the picture. This moving shadow has about the same physiological effect as flicker and is very disturbing. However, if the frame fre- quency is a multiple or sub-multiple of the power line frequency the pattern of the ripple is stationary on the image and it is much less objectionable. Therefore, since 60 cycles is standard in American power distribution systems, 30 frames per second has been chosen as standard for the frame frequency; since this is the smallest sub- multiple of 60 whose double is above the maximum flicker frequency observable by the eye.
Among other matters requiring standardization are the synchroniz- ing operations at both the transmitter and receiver. It is clear that scanning at the transmitter and receiver must be exactly synchronous to within an extremely small error. In order to accomplish this, synchronizing signals are always transmitted with the picture signals. The purpose of these synchronizing signals is to start the scanning of both the lines and frames at exactly the right time. A detailed investigation of synchronizing signals would be out of place here, but it may be stated as absolutely essential that the type of synchron- izing signal transmitted should be completely standardized.
The decision as to which was the most desirable synchronizing signal was one of the most difficult of all questions which confronted the Television Standardizing Committee. The signal shown in Fig. 9 was ultimately fixed as standard. This synchronizing signal is described as of the "serrated vertical" type. It is believed that with the use of this signal, the most stable and accurate synchronization can be obtained. Furthermore, considerable latitude is offered to the designer as to the means chosen for utilizing the signal.
The next subject which we wish to consider is the frequency chan- nel width required in television. It may be shown1 that in order to transmit the available intelligence in a television picture with N scanning lines per frame, and a frame frequency of F, a minimum fre- quency range from zero to
2 m
is required. In this equation R is the aspect ratio. Substituting into equation 1 the values which have been standardized, we get
Jan., 1939] THE ROAD AHEAD FOR TELEVISION
27
28 I. J. KAAR [j. s. M. P. E.
Thus for effective utilization of the intelligence available from a standard television picture, there must be complete and undistorted transmission of all frequencies from zero to at least 2,750,000 cycles. If this signal is used to modulate a radio frequency carrier, an ex- tremely wide frequency channel is obviously required.
In order to economize on the use of the frequency band thus re- quired, single side-band transmission is proposed. The system may more properly be termed "sesqui-side-band." In this system, the elimination of one side-band is achieved by the use of band-pass niters which have a range of partial transmission in the region on either side of the transmission band. The carrier may be placed in one of these edge bands at a point where there is approximately 50 per cent transmission. It may be shown that such a system has essen- tially double side-band transmission for very low frequencies, and single side-band transmission for medium and high frequencies. To return now to the question of utilization of the frequency channel, it is noted that by means of "sesqui-side-band" transmission the fre- quency band required by the picture signal is reduced by almost 50 per cent.
In transmitting television programs, it has been found desirable to transmit the picture and sound in the same channel. This allows a single oscillator to be used for both sight and sound in a superhetero- dyne television receiver, thus greatly simplifying tuning. In this system, the sound and sight signals are separated by selective circuits in the intermediate frequency amplifiers. Fig. 10 is a diagram of a typical television receiver, showing how it transmits and separates the picture and audio signals.
In order to design television receivers, it is necessary that the rela- tive positions of the audio and picture signals be accurately known. In order that this should be possible, the following standards have been set :
Television Channel Width. — The standard television channel shall not be less than 6 megacycles in width.
Television and Sound Carrier Spacing. — It shall be standard to separate the sound and picture carriers by approximately 4.5 MC. This standard shall go into effect just as soon as "single side-band" operation at the transmitter is prac- ticable. (The previous standard of approximately 3.25 MC shall be superseded.)
Jan., 1939]
THE ROAD AHEAD FOR TELEVISION
29
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CD!
30
I. J. KAAR
[J. S. M. P. E.
Sound Carrier and Television Carrier Relation. — It shall be standard in a tele- vision channel to place the sound carrier at a higher frequency than the television carrier.
Position of Sound Carrier. — It shall be standard to locate the sound carrier for a television channel 0.25 MC lower than the upper frequency limit of the channel.
In addition to the standards already mentioned, there are certain other standards which have been adopted, and these will be com- mented upon briefly. Thus :
It shall be standard in television transmission that black shall be represented by a definite carrier level independent of light and shade in the picture.
This means that the background level is transmitted in a television signal, thereby eliminating the need for readjustment of the receiver
FIG. 10. A typical television receiver.
when the scene being televised changes from a preponderance of white to a preponderance of black.
It shall be standard for a decrease in initial light intensity to cause an increase in the radiated power.
A technical description of this standard is to say that the polarity of the transmission is negative. It is seen that a choice exists so it is necessary that this point be standardized, otherwise the picture tube at the receiver would frequently show the equivalent of a photographic negative. Even more important than this is the fact that unless the receiver were built for the polarity of transmission sent out by the transmitter, the synchronizing signals would not be effective.
Jan., 1939]
THE ROAD AHEAD FOR TELEVISION
31
Percentage of Television Signal Devoted to Synchronization. — If the peak ampli- tude of the radio frequency television signal is taken as 100 per cent, it shall be standard to use not less than 20 nor more than 25 per cent of the total amplitude for synchronizing pulses.
Transmitter Modulation Capability. — If the peak amplitude of the radio-fre- quency television signal is taken as 100 per cent, it shall be standard for the signal amplitude to drop to 25 per cent or less of peak amplitude for maximum white.
Transmitter Output Rating. — It shall be standard, in order to correspond as nearly as possible to equivalent rating of sound transmitters, that the power of
TABLE II
Some American Picture Tube Characteristics
|
Normal |
||||||
|
Operating |
Type |
|||||
|
Overall Tube |
Anode Voltage |
Spot |
De- |
Ify*P*e |
||
|
Diameter |
Length |
Size |
flec- |
Focus- |
||
|
(Inches) |
(Inches) |
(Volts) |
(Lines) |
tion |
ing |
Remarks |
|
3 |
ny» |
1,500 |
250 |
5-5 |
5 |
Green Screen |
|
White Screen |
||||||
|
5V4 |
157/8 |
1,500-2,000 |
375-425 |
5-5 |
5 |
Green Screen |
|
White Screen |
||||||
|
5 |
153/4 |
3,000 |
450 |
M-M |
5 |
Yellow-Green |
|
Screen |
||||||
|
White Screen |
||||||
|
9 |
21 |
6,000 |
450 |
M-M |
5 |
Yellow-Green |
|
Screen |
||||||
|
White Screen |
||||||
|
12 |
24V2 |
6,000 |
450 |
M-M |
5 |
White Screen |
|
4" Projection |
14V2 |
20,000 |
450 |
M-M |
S-M |
Green or Yellow |
|
Green Screen |
* M-M — magnetic deflection both ways.
5-5 = electrostatic deflection both ways.
** 5 = electrostatic focusing.
S-M = combined electrostatic and magnetic focusing.
television picture transmitters be nominally rated at the output terminals in peak power divided by four.
Relative Radiated Power for Picture and for Sound. — It shall be standard to have the radiated power for the picture approximately the same as for sound.
The last four standards related particularly to output powers and power ratings, and while they are important in regulating the design of transmitters and receivers, they are not intimately connected with picture quality, which is of principal concern here.
32 I. J. KAAR (j. s. M. p. E.
THE TELEVISION PICTURE
When television is discussed by the public, the questions most fre- quently asked are "How good is television?" "How good will it be?" and "How much will it cost?" The answers to these questions involve such matters as : How large will the picture be ? How bright will it be? How much detail will it show? How clear will it be? A discussion of these considerations will be of interest.
The standard high-quality television system which will possibly be commercialized shortly will have a 12-inch tube with a 7!/2 by 10-inch picture. Three, 5-, 7-, and 9-inch tubes will probably also be standard commercial sizes. Compared with the size of a motion picture or even a home movie, these dimensions seem small. How- ever, considering the fact that the audience viewing a television picture will ordinarily not be more than perhaps four feet from the screen, and in the case of the small tubes, even one foot from the screen, these sizes do have considerable entertainment value. Any- one who has seen good pictures on 9-inch or 12-inch tubes will testify that when the program is interesting, the observer forgets that he is viewing television and becomes completely absorbed in the action on the screen. Nevertheless, it is reasonable to expect larger pictures in the best systems of the future. Table II shows the characteristics of some present-day television tubes.
The matter of increasing the size of the cathode-ray picture pre- sents some serious obstacles. As tubes become larger they also be- come longer and their overall size becomes such that it is difficult to find suitable cabinets for them, which at the same time lend them- selves to attractive styling. For this reason, when a 12-inch tube is used, it is invariably mounted vertically in a cabinet, and the pic- ture is seen as a mirror image by the observer. Since a mirror causes a loss of light, and possible double images and distortion, it is an un- desirable adjunct at best. As a further difficulty, as cathode ray tubes are increased in size, they require more driving power, which is expensive, and higher anode voltages, which besides the additional cost, also represents a shock hazard. Thus the prospect of making cathode-ray tubes for home use with screen diameters exceeding 12 or possibly 15 inches does not seem promising at this tune.
As an alternate method of increasing the size of the picture obtain- able by electronic means, the projection picture tube may be con- sidered. In this case a very brilliant picture on the screen of a 4-inch cathode-ray tube is enlarged by an external optical system and is
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 33
projected on a screen to a size of, say, 3X4 feet. This system re- quires an exceedingly bright tube with a very fine spot. The ultimate size of projection tube pictures is limited, on the one hand, by the brightness obtainable from a fluorescent screen without causing its rapid deterioration and, on the other hand, by the detail which can be obtained which is closely associated with the fineness of the spot achievable. Projection tube apparatus is probably too large, compli- cated, and costly for home use, but for public performances of tele- vision programs, it undoubtedly has a future.
Mechanical television systems have also been used for obtaining large pictures, with some degree of success. Of these, probably the most noteworthy is the system employed by Scophony. This system accomplishes modulation of the light-wave by utilizing fringe light, produced by virtue of passing a primary beam through a glass vessel in which is held gasoline or benzine, the liquid being subjected to vibration from a quartz crystal. The resulting modulated wave is then reflected successively by two rotating mirrors at right angles for accomplishing line and frame scanning. In the system as pro- posed, the line mirror rotates at a speed somewhat faster than 30,000 rpm.
Closely associated with the problem of picture size is the problem of picture detail. As has been pointed out, the vertical detail resolv- able in a picture depends upon the number of scanning lines, and the horizontal detail depends upon the ability of the electrical system to pass extremely high frequencies. In addition to this, of course, neither can go beyond the effective diameter of the electron spot. Observers have found that if the diameter of a picture element sub- tends less than one minute of arc at the eye, a picture contains essen- tially all the detail resolvable by the observer. If the observer is con- sidered to be 4 feet from the screen, a simple calculation will show that there are required 70 lines per inch and at 2 feet, 140 lines per inch. In present-day high-quality pictures on a 12-inch tube, with a 71/z inch X 10-inch picture, and 400 useful lines,* there are 53 lines to the inch. It is not unreasonable, therefore to expect the number of lines in television pictures to be a matter for attention in the years to come.
Goldsmith states that a high-quality motion picture screen has 5,000,000 picture elements. This would be equivalent to a 2000-line
* Ten per cent of the 441 lines must be considered lost in the retrace interval.
34 I. J. KAAR [j. s. M. P. E.
picture, which would give 1 degree resolution on a picture 3 feet X 4 feet in size, viewed from a point 5 feet away. While it is not too much to expect such television pictures sometime in the future, certainly a great many problems must be solved first. For example, such a picture would require 150,000,000 picture elements per second, which, at a conservative estimate, would need a band width of 80 megacycles per program for its transmission. This would undoubtedly require the use of quasi-optical carrier frequencies and the whole problem would entail development in many fields. To make this statement more striking, the band required would be 80 times as wide as the whole spectrum now allocated to all broadcasting in the United States.
Another important consideration in television development is the problem of picture brightness. Cathode-ray tubes used in television receivers at present, are as bright as could be desired in a darkened room. Viewed in the daylight, however, or even in a well-lighted living room, their brightness is deficient. While it is always possible to darken motion picture theaters, television receivers will probably be expected to be more versatile, and to operate in bright light as well.
The problem of increasing picture brightness is being attacked in many ways. Operating voltages, for instance, can be and are being increased. This, however, is undesirable from the standpoint of safety and cost. More efficient luminescent materials are, of course, the most obvious solution, and such materials are constantly under development.
Another interesting development in this connection is the direct- viewing tube. This differs from the ordinary tube in that the bom- barded side of the screen is viewed, instead of the opposite side, as is customary. Such tubes naturally require a construction of unortho- dox shape. However, they may be the tubes of the future, both for reasons of brightness and also for reasons of contrast and detail, as will be pointed out later. Maloff 2 reports a direct-viewing tube having a maximum useful brightness of 100 candles per square-foot. This is more than ten times as bright as the highlights in a high-quality motion picture.
Finally, there must be considered the matters of contrast and detail. The present contrast available in television tubes is quite good, but much still remains to be done. For one thing a cathode-ray tube exhibits the phenomenon of halation. This is the optical effect of the diffusion of light in the screen material, and with it we may also
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 35
group the internal reflection of light from the walls of the tube. Halation is well known in photography. It decreases the brightness of highlights and diffusely lights up points which are supposed to be dark, particularly in locations near the highlights. The general effect is thus to decrease the available contrast and to limit the possible fine detail. The direct- viewing tube is a very effective means of decreas- ing halation. When such a tube is used, the increased contrast is very striking.
In addition to halation, a cathode-ray tube also exhibits the phenomenon of "blooming," which is an electrical effect and results in defocusing the spot in the highlights. Improved focusing arrange- ments can be used to decrease "blooming," but even in the best of modern tubes it is still a problem. Since the contrast desired in a television picture requires an electronic beam of varying density, the focusing of the tube must be so arranged that the focal point does not change with current density, i.e., brilliance. This is not an easy prob- lem. However, it is evident that before the 2000-line pictures men- tioned above are ever obtained, great advances must be made in the cure of "blooming."
PROPAGATION
The problem of signal propagation in television assumes an im- portance which, in many respects, is far more serious than that of the corresponding problem in sound transmission. In the first place, the exceedingly wide frequency channels required in television make it necessary that the signals be transmitted in the ultra-short-wave bands. At these frequencies, as is well known, there exists reliably only line-of -sight transmission, since there is no longer reflection from the Heaviside layer. While this fact limits the area of coverage of any transmitter, it is actually very desirable from the standpoint of interference. Thus there is far less likelihood of multiple images caused by multiple path reception, due to reflections from the Heavi- side layer, or of interference from a distant station operating at the same frequency, or from atmospheric "static." The only serious sources of noise at these frequencies are those generators within ap- proximately line-of -sight, of which noteworthy examples are automo- bile ignition systems and medical diathermy machines.
While reflections from the Heaviside layer are negligible, neverthe- less, because of the very short waves employed, objects such as steel buildings, water towers, overhead wires, etc., provide efficient re- flectors and give rise to "ghost" images. The severity of this problem
36 I. J. KAAR [j. s. M. P. E.
will be realized much more fully than at present when the general public begins the erection of receiving antennae and the operation of receivers on a large scale.
The line-of -sight limitation greatly increases the difficulty of serv- ing a large geographical area with a given program. A brief con- sideration of this problem will be of interest. It can logically be di- vided into two parts:
(1) The conditions necessary for adequate coverage of the line-of -sight area,
and
(2) The problems involved in network distribution.
As a first step in finding the conditions necessary for adequate coverage of the line-of -sight area, we recall the formula
S = V2r [Vh~i + VM = 3560 (VJh + Vfh] (3)
where
5 = distance over which line-of -sight transmission takes place (in meters) h\ = height above intervening ground level of transmitting antenna (in meters) h2 — height above intervening ground level of receiving antenna (in meters) r = the radius of earth (in meters)
This formula can readily be derived by geometrical consideration of the curvature of the earth. Next consider the formula3 for the field- strength, near the horizon, from a transmitting antenna :
E = voltspermeter (4)
Xr2
where
E = the field strength
h = height of the transmitting antenna (in meters)
a = height of above effective ground of the receiving antenna (in meters)
T = distance of transmissions (in meters)
X = wavelength (in meters)
W = effective* radiated power from the transmitter (in watts)
Now it is reasonable to expect a transmitting antenna to be located about 300 meters above ground and a residential receiving antenna to be a half-wave dipole located 4 meters above the roof (effective ground) while the roof itself is ten meters above ground. Under these circumstances there results from equation 3:
S = 3560 (V300 + Vl4) = 75,000 meters
= 75 km. or 46.6 miles (5)
* If a transmitting antenna other than a half -wave dipole, such as a directional array, is used, the effective value of W may be increased in certain directions.
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 37
This is the radius of the area over which reliable coverage can be ob- tained from the transmitter, provided that the power of the trans- mitter is sufficiently great. Consider, now what this transmitter power must be, in order to give reliable reception at the distance S from the transmitter.
It is an empirical fact that reliable reception of a television pro- gram requires an input signal of about one millivolt. Now the effec- tive height4 of the usual half -wave dipole receiving antenna is X/x. Therefore, the required transmitter antenna power is given by the equation :
88\/W ah \ in_, -J35- ' - = 10
or
W = 1 28 X lO-' JP_ .= 1.28 X10-9 (75,000)* a2/*2 42 X (300)2
= 27,100 watts* or 27.1 kw. (6}
Actually, at the present time it is not feasible to radiate this much power, since no satisfactory tubes are available to generate it at these ultra high frequencies.
Using two of the latest high-power developmental tubes in push- pull, it is possible to generate 10 kw. (40 kw. peak) at fifty megacycles. The limiting factor in this case is the fact that the size of high power tubes makes it impossible to tune them above a certain critical fre- quency and their high interelectrode capacities make it difficult to load them properly and still preserve the desired band-pass character- istics. Thus with tubes of the present types, it is not yet possible to reach the desired power level; and the condition will become more serious as more of the still higher frequency channels are used for television. However, it is reasonable to expect that the ingenuity of tube designers will overcome this difficulty in the next few years. In the meantime, the condition can still be corrected by increasing the height of the transmitting antenna, and especially of the receiving antenna.
As a result of the above, an interesting fact is evident. If the height of the receiving antenna is neglected in calculating the line-of -sight distance, there results :
5 = 3560 vT * Slightly in error because formula 4 is extrapolated beyond the horizon.
38 I. J. KAAR [J. s. M. P. E.
Substituting this value of 5 into equation 6 there results :
It is evident that this value of W is independent of h. In other words, it requires 12.9 kilowatts of transmitted power to generate a signal of one millivolt in a half -wave dipole 4 meters above the ground at the horizon. This value is independent both of the carrier frequency and of the height of the transmitting antenna. The latter result is
FIG. 11.
The effect of multiple-path transmission or reflection upon the received image.
very surprising. It indicates that as the antenna height is increased, the same power still suffices to reach the horizon — the increased dis- tance being just compensated by the increased antenna height.
Another problem of considerable importance in the adequate cover- age of the line-of -sight area is the elimination of multiple reception or echoes. This problem is of practically no importance in sound broadcasting. To get a clear idea of the problem, suppose that in addition to the direct ray travelling from the transmitting to the re- ceiving antenna there is also a ray which reaches the receiving an- tenna by way of reflection from a large building. This reflected ray
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 39
will have travelled a greater distance than the direct ray before reach- ing the receiver. The picture which it carries will therefore be re- tarded in time, and it will consequently cause a similar but slightly displaced picture to appear next to the desired picture. This is a very annoying effect, and great effort must be made to avoid it. This effect is illustrated in Fig. II.5
The path difference necessary to cause a disturbing echo can be easily computed. The time of retardation of the reflected ray is clearly equal to the difference in path of travel divided by the velocity of light. Then, remembering that the electron beam scans (4/s X 30 X 441 X 441) picture elements per second, the displacement of the echo from the main picture (in picture elements) is
D = 4/3 X 30 X 441 X 441
3 X 108 = 0.026 times the path difference in meters
In other words, a path difference of 127 feet will cause an echo dis- placement of one picture element. This is enough to detract from the quality of the picture.
The elimination or reduction of echoes is a complicated problem. In metropolitan areas, due to the presence of many reflectors in the form of tall buildings, the problem is serious indeed. The usual solution is to use a directional antenna which will discriminate against the undesired signal. Horizontal polarization of the radiated signal has been found to improve the signal-to-noise ratio at television car- rier frequencies, and its use will therefore probably become a standard practice.
Some of the problems connected with the chain distribution of television programs may now be considered. There are two general methods which have been used to transmit television programs from a key transmitter to a distant transmitter. These are the use of (1) the radio relay or (2) the coaxial (or other) high-fidelity cable relay.
Whichever method is used, the relay stations must be sufficiently close together so that non-fading noise-free signals are received at each repeater location. It has been found that relay stations must be located from 30 to 70 miles apart, the exact distance depending on noise conditions and (in the case of the radio relay) on the topography of the landscape. It has been customary to operate radio relays at wavelengths of two meters or less. Each relay station, of whichever
40 I. J. KAAR [j. s. M. P. E.
type, must reproduce the incoming signal with the highest fidelity, having neither amplitude, frequency, nor phase distortion. In other words, the picture must not be degraded in passing through the re- lays.
It is not surprising that the great problem in the relaying of tele- vision signals is cost. The cost per mile of a coaxial cable required to handle the exceedingly wide frequency bands of television programs is, at the present time, many times as great as the cost of correspond- ing networks used in sound broadcasting, both as regards initial cost and maintenance. If radio relaying is used, the cost of the relay trans- mitters required is obviously very great. However, the coming years are likely to bring great reductions in the costs of both methods of relaying, particularly the coaxial cable.
This paper has been an effort to point out the fact that many problems still must be solved before fully satisfying television pic- tures will be available in the home. However, it is not to be con- strued that the commercial introduction of television will await a solution to these problems. Undoubtedly television will be com- mercialized in the near future and the problems will be solved as time passes — much the same, for instance, as was the case in the mo- tion picture industry. One fact is very clear, that the further de- velopment of television must come largely through findings in the field, that is, by actual trial.
The author wishes to acknowledge the assistance of Dr. Stanford Goldman in the preparation of this paper and the courtesy of the Na- tional Broadcasting Company and the British Broadcasting Com- pany for the use of photographs of their equipment.
REFERENCES
1 WHEELER, H. A., AND LOUGHREN, A. V. : Proc. I.R.E., 26 (May, 1938), No. 5, p. 558.
2 MALOFF, I. G.: RCA Review, 2 (Jan., 1938), No. 1, p. 291.
3 BEVERAGE, H. H.: Monograph "Television," RCA Review, 2 (1938), p. 99.
4 HUND, A.: "Phenomena in High-Frequency Systems," p. 466. (McGraw- Hill.)
6 SEELEY, S. W. : "Effect of Receiving Antenna on Television Reception Fidelity," RCA Review, 2 (April, 1938), p. 435.
DISCUSSION
MR. McNABB: Referring to the reproductions (Figs. 4 and 5) of a British pic- ture and an American picture, the line structure was quite evident in the British picture, but the contrast seemed a little better. Is the contrast better in the Brit- ish picture due to the method of transmission, or is the transmission of direct
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 41
current along with the signal better than the American method of adding the d-c. at the receiving end?
MR. KAAR: There is no essential difference in the method of transmission in England and here. The only difference is the means of synchronization. As far as contrast and detail are concerned, there should be no difference between the two systems except for the possible fact that we have 441 lines, whereas they have 405.
It is possible to photograph any kind of picture from the front of a picture tube and we can so adjust focus and contrast as to make the line structure visible on an American picture.
As a matter of fact, neither of these pictures is a good example because they have both been degraded by photographic processes in the original photograph, the enlargement, the negative, and the lenses, so in order to compare the two fairly the originals should actually be seen. Our pictures are somewhat better than the British pictures.
MR. FINN: In the choice of repeaters, Mr. Kaar suggested that the choice as between coaxial cables and straight etherization of a program is very close. Is it your suggestion that the coaxial cable be used, over hill and dale for thirty or sixty miles, throughout the whole broadcast circuit, to blanket the country?
MR. KAAR: That is a difficult question to answer because I am not familiar with the recent progress on coaxial cable. You will find a description of the New York-Philadelphia cable in the literature. As I remember, it has repeaters every ten miles and as yet will not transmit the full band required. Perhaps some day transcontinental cables may be laid capable of handling television programs, but I can not say that they will. The other system is satisfactory and has been tried. As to the economic balance between the future use of cables and ether channels, that still remains to be answered.
MR. GOLDSMITH: The New York-to-Philadelphia cable was said to have cost $540,000. Whether that included large engineering developmental expenses or not, it is now known. In any case, that would have indicated a per-mile cost of $5000 or $6000. The major broadcasting networks in the United States today use somewhere on the order of 40,000 or 45,000 miles of lines, and if one multiplies that by $5000 for the cost of laying a similar coaxial cable network, the result of the multiplication is an extremely large and uneconomic amount.
However, it is believed likely that development will lead ultimately to less costly coaxial cables with repeater stations closer together and satisfactory for the purpose, or to economic radio relay systems that will work very effectively.
MR. KAAR: The fact that such a serious problem exists in chain programs comes pretty closely home to the motion picture engineer, because for the immediate present there is an answer to the chain broadcasting of television programs, namely, the transmission of motion picture films, which will undoubtedly be done extensively.
MR. GOLDSMITH: There are many practical and artistic reasons why film will necessarily be widely used.
MR. WILLIFORD: Does the adoption of the 60-cycle frequency as standard mean that communities having 25- or 50-cycle power supply are definitely out of the picture as far as television is concerned?
MR. KAAR: There is no connection between the synchronizing mechanism of television and the power frequency. The synchronizing is accomplished by
42 I. J. KAAR [j. s. M. P. E.
transmitted signals. The only reason for and the advantage of choosing a frame frequency that is a multiple or submultiple of the power-line frequency is this: If a system should develop a ripple, as we know it in audio work, that ripple would occur at power-line frequency. If the frame frequency occurred at some other frequency than that, this ripple, which would be either a light area or a dark area, would travel across the screen. If the system is perfect and there is no ripple, it makes no difference at all. This is simply chosen as a safety measure.
MR. GOLDSMITH: If the power-supply system of the receiver and its shielding are so engineered that no such effects appear, the receiver can be used equally well regardless of the power supply.
MR. CABLE: It seems to me that the frequency chosen as 30 places a definite limitation on the picture brightness, because the frequency is a function of bright- ness.
MR. GOLDSMITH: The present standard is 60 pictures per second. We see 60 "half pictures," with interlaced scanning. First is shown a picture with lines 1, 3, 7, and so on, as a full picture; and the one with lines 2, 4, 6, 8, and so on, as the next picture, a sixtieth of a second later. So the frame frequency is 30 but the field frequency is 60 per second. You substitute for picture flicker a new effect called inter-line flicker, which is practically invisible.
MR. FRIEDL: In selecting the number of frames projected, you have evidently regarded power-supply frequency as an important factor. Inasmuch as the mo- tion picture film will be used as a means of widely distributing the program, the frame-frequency of the motion picture is a consideration. I would judge, from the decision, that the more difficult matter of control is the power supply, but we as motion picture engineers naturally ask why the 24-frame frequency with in- terlacing to give 48 images was not considered the more important factor.
You speak of standards in television. We are very standards-conscious in the SMPE and are aware of the importance of international as well as national stand- ardization. I see a lack of uniformity among the standards adopted by Germany, Great Britain, France, and America. That might be excused at the moment be- cause of the fact that the range of transmission is so limited and we can not expect immediately to transmit across the ocean; but inasmuch as the number of lines selected is 441, which has been selected mainly to allow room for improvement, can not we also anticipate improvement and have confidence in the effect of the de- velopment to look forward to transmission across the ocean, and, therefore, inter- national standardization?
MR. GOLDSMITH: We may hope for this, because some such standard as 441 lines for the picture might be adopted by all the nations. But it must be ad- mitted that at the present time radio differs from motion pictures in that interna- tional standardization is rather conspicuously absent. However, it may come with television.
MR. FRIEDL: We are conscious of the high voltages in the larger tubes — 25,000 and 40,000 volts. What is the voltage on the 12-inch tube and how does the sys- tem meet with the protective requirements of the NFPA and the Fire Under- writers?
MR. KAAR : The voltage on the 12-inch tube will probably be 6000 volts. That sounds like a very serious matter, but really it is not. If you sit in a dentist's chair and he turns the X-ray on you, that is about 40,000 volts. It is protected.
Jan., 1939] THE ROAD AHEAD FOR TELEVISION 43
It simply means we have a job of protecting the television receiver, possibly by an interlocked back.
MR. FRIEDL: All I can say is that conditions in the home where children might come in contact with the apparatus are different from what they are in a dentist's office.
MR. GOLDSMITH: The back of the receiver is an expanded metal mesh. If you open the back, you will open all power circuits and discharge the high-voltage condensers automatically. If you try to take the cathode-ray tube out you will similarly open up the circuits. You can not get into contact with a high voltage. It is generally so arranged that even people with screw-drivers and determination simply can not get into trouble, and we hope these practices will continue.
MR. FRIEDL: Does horizontal polarization mean that the antenna will be hori- zontal? Also, is that discussion of a three-meter receiving antenna going back to a multiplicity of "wash line" antennas on every roof?
MR. GOLDSMITH: The antenna wire or rod is only about six feet long. The two component rods are each about three feeet long.
MR. KAAR: They are half a wavelength long, and the wavelengths are of the order of five meters.
MR. McNABB: In an article about six months ago in Electronics, regarding the quality of television pictures, it was the opinion of certain American engineers who investigated the British pictures that the British were ahead of us in their technical developments as well as their commercial exploitation of the art. That seems to disagree with the opinions of other American engineers. Exactly what are we to believe?
MR. GOLDSMITH : The consensus of engineering opinion among those who have seen television pictures in London and New York is that there is little if anything to choose between them. It is most unlikely that practice in either case is far ahead of the other.
REPORT OF THE STUDIO LIGHTING COMMITTEE*
Summary — In a previous report of the Studio Lighting Committee the need of a catalogue of studio lighting equipment was emphasized. A number of papers have been published which describe various lamps and light-sources in detail, but there has not been assembled in one paper a symposium of all types of equipment and light- sources used on motion picture sets.
This report covers all types of equipment in general use. The various lighting units are numbered and briefly described. Photographs of popular lamps are shown. Tables give minimum and maximum beam divergences, carbon and bulb sizes. Reference numbers are assigned to the various lamps for convenience in listing their characteristics. Data on light control devices and lamp filters are included.
CARBON ARC LAMPS
(1) MR Type 27 Scoop. — Chromium plated reflector and Factrolite glass diffuser. Solenoid controlled. A twin-arc flood source, used for overhead illumination of walls, backings, and other areas that can not be lighted satisfactorily by spotlamps. Suspended singly or in groups. A smooth, general-purpose light-source.
(2) MR Type 29 Broadside. — Chromium plated reflector and Factrolite glass diffuser. Solenoid controlled. A twin-arc flood source that may be raised, lowered and tilted, and used as a floor-lighting unit for building up front light to the desired exposure level.
(3) MR Type 40 Duarc Broadside. — Chromium plated reflector and pebbled, sand-blasted Pyrex glass diffuser. An unproved motor- controlled twin-arc flood-lamp that takes the place of both scoop and broadside of the older types.
(4) MR Type 65 Arc Spotlamp. — Eight-inch diameter Fresnel- type lens. High-intensity rotating mechanism. Used for front and back lighting, close-up and medium shots. The intensity is almost uniform in the main portion of the beam, tapering off at the edges to permit overlapping adjacent beams without producing objection- able high-intensity zones. Within its energy capacity this lamp may be used for all photographic spot lighting.
(5) MR Type 90 Arc Spotlamp. — Fourteen-inch diameter Fresnel- type lens. High-intensity rotating mechanism. Used for back
* Presented at the 1938 Fall Meeting at Detroit, Mich. 44
STUDIO LIGHTING COMMITTEE REPORT
45
FIG. 1. Typical high-intensity rotating element.
UPPER CARBON ACTUATING LEVER
INDUCTIVE RES. N0.2 INDUCTIVE RES. NO. I
FIG. 2. Typical solenoid feed mechanism.
46
STUDIO LIGHTING COMMITTEE REPORT [j. s. M. p. E.
Lamp No.
1. MR type 27 scoop.
2. MR type 29 broadside.
3. MR type 40 duarc broadside.
Jan., 1939]
STUDIO LIGHTING COMMITTEE REPORT
47
lighting, sunlight effects through doorways or windows, etc., for key lighting on sets of moderate size, and for general front lighting into the rear areas of deep sets.
(6) MR Type 170 Arc Spotlamp.— Twenty-inch diameter Fresnel- type lens. High-intensity rotating mechanism. Used for back, cross, and key lighting, and for wide- and narrow-angle front and effect
Lamp No.
4. MR type 65 arc spotlamp.
5. MR type 90 arc spotlamp.
6. MR type 170 arc spotlamp. 8. 36-inch sun arc.
lighting. This unit has wider use for both black-and-white and color photography than any of the other arc units.
(7) 24-Inch Sun Arc. — Twenty-four inch diameter glass mirror. High-intensity rotating mechanism. Normally used with the arc crater facing the mirror and a clear glass door on the front of the lamp house. Where very sharp shadows are necessary the clear glass door may be moved to the position normally occupied by the mirror. A metal door is then placed on the open end. A large number
48 STUDIO LIGHTING COMMITTEE REPORT [J. S. M. P. E.
of these lamps have been converted to use the same optical system as the MR type 1 70 lamp . Used for back lighting, sunlight effects through windows and doorways, etc., for key lighting on sets of moderate size, and for general front lighting into the rear areas of deep sets.
(8) 36-Inch Sun Arc. — Thirty-six inch diameter glass mirror. High-intensity rotating mechanism. Similar to the 24-inch Sun Arc except as to size. The 24-inch Sun Arc is rapidly being converted to the use of the Fresnel type of lens, but due to its great penetrating power, the 36-inch Sun Arc is valuable on extremely long throws and retains its popularity in its present form. When a large quantity of
diffused light is required from this unit, a diverging door composed of strips of cylindrical lenses replaces the plain glass door. The lamp is used where a very high intensity of pro- jected light is required, as in back lighting behind a high level of fore- ground illumination; or where well denned shadows are required ; or where a clearly defined streak of light is required through the general illumina- tion; or for producing a general illu- mination of great penetration and high intensity.
fl ~~J* ^ so~AmPere Rotary Arc Spot-
lamp. — An 8-inch diameter plano-con- Lamp No. 10.
vex condenser or 12 -inch Fresnel-type
lens. High-intensity rotating mechanism. One of the early high- intensity arc spotlamps. This lamp is not suitable for color in its present form because of the spectral energy distribution of the carbon trim. A number of these lamps have recently been converted to the use of 11 mm. X 20-inch H. I. motion picture studio positive carbons to make them suitable for color photography. Used for back lighting on black-and-white sets and to increase the intensity of illumination at any point where projected light is required within the range of its intensity.
(10) B & M Type 9 Twin-Arc Broadside.— Chromium plated re- flector and glass diffuser. Solenoid striker with direct motor feed. A twin-arc flood source that may be raised, lowered and tilted, and used as a floor-lighting unit for use in building up front light.
Jan., 1939] STUDIO LIGHTING COMMITTEE REPORT 49
TABLE I
Arc Lamps for Set Lighting
Ppsi- Nega-
*Degrees Beam tive tive
Lamp Divergencies Carbon Carbon
No. Unit Min. Max. No. No.
1 MR 27 Scoop1 90 90 1 10
2 MR 29 Broadside1 90 90 1 10
3 MR 40 Broadside 90 90 1 10
4 MR 65 Spotlamp* 8 44 2 11
5 MR 90 Spotlamp3 8 44 5 14
6 MR 170 Spotlamp2 8 48 6 15
7 24-Inch Sun Arc2 **10 24 6 13
8 36-Inch Sun Arc^ 10 32 6 13
9 80- Amp. Rotary Spot* **8 30 4 12 94 80- Amp. Rotary Spot
(Converted) 8 44 3 12 10 B & M Type 9 Twin- Arc Broadside 90 90 1 10
* Approximate figures referring to usable photographic light. ** With Fresnel-type lens divergences are approximately 8 to 44 degrees.
TABLE II
Carbons for Set Lighting
Car- bon Arc
No. Positive Carbons Amperes Volts
1 8-Mm. X 12 NP MP Studio2'"'7'"'" 38-43 35-40
2 9-Mm. X 20" Hilow Projector6'9 65-70 52-54
3 11-Mm. X 20" HI MP Studio9 90-95 62-65
4 1/2* X 12" 80- Amp. Rotary Spot2'7'8'9 75-80 50-55
5 13.6-Mm. X 22" HI Projector4'5'9 110-115 54-56
6 16-Mm. X 20" HI MP Studio2'4'5'7'8'9 140-150 64-67
Negative Carbons
10 8-Mm. X 12" NP MP Studio
11 7-Mm. X 9" Cored Suprex Negative
12 Vs" X 9" Cored 80-Amp. Rotary Spot Negative
13 11-Mm. X 10" Plain-Cored MP Studio Negative
14 3/s" X 9" Cored Orotip Negative
15 7/18" X 9" Cored Orotip Negative
50
STUDIO LIGHTING COMMITTEE REPORT [j. s. M. P. E.
Lamp No.
20. MR type 36 studio spotlamp.
21. MR type 26 studio spotlamp.
22. MR type 16 cinelite.
23. MR type 45 rifle lamp.
24. MR type 220 18-inch sun spot.
25. B & M type T5 studio spotlamp.
Jan., 1939]
STUDIO LIGHTING COMMITTEE REPORT
51
INCANDESCENT LAMPS
(20) MR Type 36 Studio Spotlamp—A 6-inch diameter, 9-inch focus plano-convex condenser. For use where a full controlled beam of light is required: in close-up photography for back and close lighting, particularly where the photography demands high contrast of light and shadows ; in general motion picture set lighting it is use- ful for special effects and for illuminating areas that can be reached only by projected light.
(21) MR Type 26 Studio Spotlamp. — A spherical mirror is adjust- ably mounted behind the bulb to collect the rays of light and direct them upon an 8-inch plano-convex
condenser. Used for back lighting, special effects, and particularly on sets where the general lighting must be in low key.
(22) MR Type 16 Cinelite.—A spun aluminum reflector, finished inside by wire brushing and chemical treat- ment, which gives it a diffusing characteristic. Used where light portable equipment is required.
(23) MR Type 45 Rifle Lamp.— Stamped metal reflector, chromium- plated with rifled corrugations for diffusion Used for general floor lighting.
(24) MR Type 220 18-Inch Sun
Spot. — An 18-inch diameter parabolic glass mirror or faceted metal reflector, with spill ring as standard adjunct. Used for general illumination, for back lighting and cross lighting in small and moderate size sets, and for projecting light into back areas of sets.
(25) B&M Type T5 Studio Spotlamp.— A short-focus Fresnel-type lens in front of the bulb and a small fixed spherical mirror behind the bulb project light forward into the field. This, in combination with the light projected around the lens from the 24-inch reflector, gives an even, intense light. For the large mirror, either a 24-inch diame- ter aplanatic reflector or a 10-inch focus glass mirror is used. The aplanatic reflector produces a very even field of light. Greater pene- trating power for long throws may be obtained with the parabolic
Lamp No. 26. MR type 226 24-inch studio sun spot.
52
STUDIO LIGHTING COMMITTEE REPORT [j. s. M. p. E.
Lamp No.
28. MR type 206 baby solarspot.
29. B & M type 6 baby keg-lite.
30. B & M type K keg-lite.
Lamp No.
31. MR type 208 solarspot.
32. MR type 210 junior solarspot.
33. MR type 214 senior solarspot.
Jan., 1939] STUDIO LIGHTING COMMITTEE REPORT 53
glass reflector. Used for back lighting, cross lighting, front lighting, and effect lighting.
(26) MR Type 226 24-Inch Studio Sun Spot.— A 24-inch diameter glass mirror, with a spill ring that allows only projected light to leave the lamp. Used for back lighting large sets, in which case the heads are removed from the pedestals and are mounted on parallels or plat- forms built at the top of the set or hung from the stage roof or ceiling.
TABLE in
Incandescent Lamps for Set Lighting
*Degrees Beam Bulb Bulb
Lamo Divergencies No. No.
No Unit Min. Max. **(B & W) (Color)
20 MR 36 Studio Spotlamp 8 44 8
21 MR 26 Studio Spotlamp 8 44 8
22 MR 16 Cinelite1* 60 60 16
23 MR 45 Rifle Lamp 60 60 4-5 15
24 MR 220 18" Sun Spot 8 18 3-7 14
25 B & M T-5 Studio Spotlamp" 8 40 2-3 13-14
26 MR 226 24" Sun Spot 12 24 2 13
27 B & M 24" Sun Spot 12 24 2 13
28 MR 206 Baby Solarspot11 8 40 9
29 B & M Baby Keg-Lite Type 6 6 45 9
30 B & M Keg-Lite Type K 4 44 3-7 14
31 MR 208 Solarspot" 10 44 8
32 MR 210 Junior Solarspot11 10 44 3-7 14
33 MR 214 Senior Solarspot 10 44 2 13
34 Sky Light™ 180 180 2 13
35 Broadside (Doubles) 90 90 5 15
36 36" Sun Spot 12 24 1 12
37 Overhead Strip Lamp 5 15
* Approximate figures referring to usable photographic light. ** For black-and-white photography.
The lamps are used where a large quantity of light is to be supplied by a small number of units ; for front lighting on deep sets ; for cross lighting where high contrast is desired or on wide sets where the camera angle requires that the cross light be projected from a dis- tance ; for effect lighting such as in simulating sunshine through win- dows or doorways, or interior light into exterior darkness in night shots ; and for similar special requirements demanding beams of high intensity.
(27) B&M 24-Inch Sun Spot.— Similar to No. 26 in design and use.
54 STUDIO LIGHTING COMMITTEE REPORT [J. S. M. P. E.
(28) MR Type 206 Baby Solarspot.—A 6-inch diameter Fresnel- type lens. The small size of this lamp permits its use in places where the larger lamps can not be accommodated, particularly where it is necessary to conceal a source of high-intensity light.
(29) B & M Baby Keg-Lite Type 6.— A short-focus 6-inch diameter Fresnel-type lens combined with a pref ocused mirror ; used for special effects and where small units are required.
(30) B & M Keg-Lite Type K— A 10-inch diameter by 6-inch focus Fresnel-type lens. A set spherical mirror projects the rear light from the bulb toward the lens. A general purpose unit within its intensity
limits; used for front lighting, back lighting, and modeling.
(31) MR Type 208 Solar spot. —An 8-inch diameter Fresnel-type lens. A rhodium-plated spherical mirror is used at the rear of the bulb to direct the light toward the lens. Used for back lighting, modeling, and general front lighting within its intensity range.
(32) MR Type 210 Junior Solar- spot. — A 10-inch diameter Fresnel- type lens. A rhodium-plated spheri-
Lamp No. 34. Sky light. J f
cal mirror is used at the rear of the
bulb to direct the light toward the lens. Used for back lighting, front lighting, cross lighting, and modeling within its intensity range.
(33) MR Type 214 Senior Solar spot. — A 14-inch diameter Fresnel- type lens. A rhodium-plated spherical mirror is used at the rear of the bulb to direct the light toward the lens. Used where high- wat- tage units are desirable, for back lighting, front lighting, and side lighting.
(34) Sky Light. — A shallow diffuse reflector about 24 inches in diameter. Used below and above sky backings and screens, where a flat even light distribution is required.
(35) Broadside (Doubles). — Two flood:type reflectors housed in one unit, used for floor, side, and overhead lighting: One of the first incandescent units made.
(36) 36-Inch Sun Spot. — A 36-inch diameter glass mirror. Used where the highest intensity of projected light is required from an incandescent tungsten source.
Jan., 1939]
STUDIO LIGHTING COMMITTEE REPORT
55
(37) Overhead Strip Lamp. — A trough-like unit containing sockets for five 1000-watt PS 52 bulbs. Used to supply fill-in light where it is difficult to use a more bulky housing.
TABLE IV
Incandescent Bulbs
Nominal
Bulb Rated
No. Watts
Nominal Amps.
Bulb** Volts Amps. Base
"MP" Type Lamps (for Black-and-White Photography)
|
1 |
10,000 |
G-9613 |
|
2 |
5,000 |
G-6413 |
|
3 |
*2,000 |
G-4813 |
|
4 |
1,500 |
PS-521* |
|
5 |
1,000 |
PS-5213 |
|
6 |
****!, 000 |
T-2013 |
|
7 |
•1,000 |
G-48 |
|
8 |
1,000 |
G-40 |
|
9 |
****500 |
T-2013 |
|
10 |
****500 |
G-30 |
|
11 |
****200 |
T-10 |
|
110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 110-115-120 |
87.0 43.5 17.4 13.1 8.7 8.7 8.7 8.7 4.4 4.4 1.7 |
Mog. Bip. Mog. Bip. Mog. Bip. Mog. Scr. Mog. Scr. Mog. Scr. Mog. Bip. Med. Bip. Medium*** Mog. Scr. Medium |
"CP" Type Lamps (for Color Photography — with Proper Filter)
(All "CP" Type Lamps Operate ar 3380°K. Color Temperature)
12 10,000 G-9611 110-115-120 87.0 Mog. Bip.
13 5,000 G-64n 110-115-120 43.5 Mog. Bip.
14 2,000 G-4811 110-115-120 17.4 Mog. Bip.
15 2,000 PS-5211 105-120 17.4 Mog. Scr,
Additional Types Frequently Used in Studio Work
16 1,000 PS-35™ 105-120 8.7 Mog. Scr.
(No. 4 Photoflood)
17 500 A-25™ 105-120 4.4 Med. Scr.
(No. 2 Photoflood)
18 250 A-21 13 105-120 2.2 Med. Scr.
(No. 1 Photoflood)
* Available also in Mogul screw base for older equipments. ** G = spherical, PS = pear shaped, T = tubular, A = modified pear shaped. Numbers refer to diameter in 1/8 inch.
*** Some units require the med. bip. base, others the med. scr. base or med. pref. base.
**** Used in utility lamps, lighting fixtures, table and floor lamps.
56
STUDIO LIGHTING COMMITTEE REPORT [j. s. M. p. E.
TERMS USED IN STUDIO LIGHTING PRACTICE
The terms applied to the various units of motion picture studio lighting equip- ment are legion and vary from studio to studio, and even from month to month. Sometimes a lamp is described by its type number alone; or by the rated current
Lamp No.
35. Broadside (doubles).
36. 36-inch sun spot.
37. Overhead strip lamp.
in the case of arc -spotlights; or by the kilowatt rating of incandescent units. In some instances the mirror diameter supplies the name. Below are some com- monly used terms, the "Lamp Numbers" referring to the preceding sections:
Term Broad Side Arc Sixty-Five Ninety One-Seventy Twenty-Four Thirty-Six Eighty
1000- Watt Spot Rifle Eighteen T-5
Lamp No.
2-3-35
2-3
4
5
6
7
8
9
20-21-31 23 24 25
|
Lamp |
|
|
Term |
• No. |
|
Twenty-Four Inkie |
26-27 |
|
5KW |
26-27 |
|
Baby |
28-29 |
|
Keg |
30 |
|
Junior |
32 |
|
Senior |
33 |
|
Pan or Skypan |
34 |
|
Doubles |
35 |
|
10KW |
36 |
|
Strip |
37 |
Jan., 1939] STUDIO LIGHTING COMMITTEE REPORT 57
The following are a few terms used for material and equipment associated with the use of studio lamps:
Silks. — Frames equipped with china silk diffusers, hung on the fronts of lamps to diffuse the light and reduce the intensity.
Jellies. — Frames equipped with chemically treated gelatin. Used for the same purposes as silks.
Scrim. — Black gauze used in various places to reduce intensity and diffuse light.
Diverging Doors. — Strips of cylindrical glass lenses. Used on Sun Arcs for light diffusion.
Snouts. — Various shapes of black sheet metal hangars. Used on the front of lamps to block out undesired light.
Spill Rings. — A series of sheet metal tubes, used in front of incandescent bulbs in mirror type lamps to block off angular rays emanating from the front surface of the bulb filament (see photographs of lamps 24-26).
Spot Projector. — A unit equipped with a condenser system that fits on the front of a Type 170 carbon arc lamp in place of the Fresnel-type lens; used to produce a sharply defined round spot of light.
Gobos, Flags, Cheese Cutters, Niggers, Etc. — It is often desirable to place opaque screens at various points on a set to keep all or a part of the light from reaching certain areas or objects. These screens are painted dull black and are rectangular, square, or circular, as the occasion may require.
LAMP FILTERS FOR COLOR PHOTOGRAPHY
Carbon Arc Lamps. — Carbon arc lamps 1-2—3 are used for Technicolor pho- tography without color filters. All types of high-intensity rotating arc lamps re- quire a Type Y-l straw gelatin filter.4
Incandescent Bulb Lamps. — Where incandescent bulbs are used on Technicolor photography a special blue glass filter is required along with a series of CP Type bulbs, which burn at a uniform color temperature of 3380 °K.n
REFERENCES
(All references are to J. Soc. Mot. Pict. Eng.)
1 MOLE, P.: "New Developments in Carbon Arc Lighting," XXII (Jan., 1934), No. 1, p. 51.
2 HANDLEY, C. W.: "Lighting for Technicolor Motion Pictures," XXV (Nov., 1935), No. 5, p. 423.
3 RICHARDSON, E. C. : "Recent Developments in High-Intensity Arc Spot- lamps for Motion Picture Production," XXVIII (Feb., 1937), No. 2, p. 207.
4 HANDLEY, C. W.: "The Advanced Technicof Technicolor Lighting," XXIX (Aug., 1937), No. 2, p. 169.
5 JOY, D. B , AND DOWNES, A. C.: "Characteristics of High-Intensity Arcs," XIV (March, 1930), No. 3, p. 291.
6 JOY, D. B., BOWDITCH, F. T., AND DOWNES, A. C.: "A New White-Flame Carbon Arc for Photographic Light," XXII (Jan., 1934), No. 1, p. 58.
7 BOWDITCH, F. T., AND DOWNES, A. C.: "The Photographic Effectiveness of Carbon Arc Studio Light-Sources," XXV (Nov., 1935), No. 5, p. 375.
58 STUDIO LIGHTING COMMITTEE REPORT [j. S. M. P. E.
8 BOWDITCH, F. T., AND DOWNES, A. C. : "The Radiant Energy Delivered on Motion Picture Sets from Carbon Arc Studio Light-Sources," XXV (Nov., 1935), No. 5, p. 383.
9 BOWDITCH, F. T., AND DOWNES, A. C.: "Spectral Distributions and Color- Temperatures of the Radiant Energy from Carbon Arcs Used in the Motion Picture Industry," XXX (April, 1938), No. 4, pp. 400-409.
10 RICHARDSON, E. C.: "A Wide-Range Studio Spotlamp for Use with 2000- Watt Filament Globes," XXVI (Jan., 1936), No. 1, pp. 95-102.
11 Report of the Studio Lighting Committee, XXX (March, 1938), No. 3, p. 294.
12 Report of the Studio Lighting Committee, XXV (Nov., 1935), No. 5, p. 432.
13 FARNHAM, R. E., AND WORSTELL, R. E. : "Color Quality of Light of Incan- descent Lamps," XXVII (Sept., 1936), No. 3, p. 260.
C. W. HANDLEY, Chairman
R. E. FARNHAM V. E. MILLER G. F. RACKETT
W. C. KUNZMANN M. W. PALMER E. C. RICHARDSON
J. H. KURLANDER F. WALLER
DISCUSSION
MR. GOLDSMITH: Is not this report the first assembly of such material in com- plete form?
MR. GEIB : Yes. This is the first time anyone has attempted to give a com- plete catalogue of studio lighting equipment.
MR. WOLF : Is the mercury- vapor arc lamp in commercial use?
MR. GEIB : No.
MR. WOLF: I understand they are used in Holland, in combination with sodium- vapor lamps to get a more balanced spectrum.
MR. GOLDSMITH: It would be interesting to know whether that type of com- bination could be used for color photography because while it might give a sub- jective effect of white with the addition of sodium vapor-lamps, it certainly would not give the physically continuous spectrum of an arc or an incandescent lamp.
It would therefore be interesting to know whether the Technicolor engineers could use a combination of that sort.
MR. WOLF : I understand that the combination is used a great deal in Holland for television work and for studio work.
MR. GOLDSMITH : As the pressure is increased in the mercury lamps the back- ground spectrum becomes more and more intense and a certain quasi-continuity of the spectrum is obtained.
MR. CARLSON: That is correct. As the operating pressure in the mercury arc type of lamp is increased the continuity of the spectrum is definitely improved, together with an increased output of red energy.
In the case of medium-pressure air-coole4 lamps the spectrum is still largely of the discontinuous or band type. The high-pressure water-cooled capillary lamp now on the market shows a continuous spectrum superimposed on the band spectrum. For still higher pressures the band characteristics largely disappear. Thus the mercury arcs that are now available are well adapted to monochromatic photography, but not for color work — nor is their light easily filtered because of the "humps" in the energy vs. wavelength curve. Possibly the sensitivity charac- teristics of the color film could be adapted to the light. Information on the lamp
Jan., 1939] STUDIO LIGHTING COMMITTEE REPORT 59
was published in the September, 1938, issue of the JOURNAL by Farnham and Noel.
MR. WOLF: What are the efficiencies of the light-sources now as compared with what they were, say, several years ago?
MR. DOWNES : The efficiency of light-sources in the studios is, so far as I have been able to learn, not of great importance. What is wanted is a steady light- source, and one that can be directed to the particular part of the set with cer- tainty and assurance that it is going to continue to deliver uniform amount and quality of light during the time the photographing is done.
The efficiencies in lumens per watt on the sets in the studios must vary through tremendously wide limits because of the fact that a very large number of the light- sources used are focused to deliver spots of various sizes on the set and as a result the luminous efficiencies are extremely variable. These various spot units can be focused to deliver spots from about three feet in diameter to very large ones, and it would therefore be very difficult indeed to obtain any figures for lumens per watt except with a bare light-source which, considering how they are used, would mean little or nothing.
PHOTOGRAPHIC EFFECTS IN THE FEATURE PRODUCTION
"TOPPER"*
R. SEAWRIGHT AND' W. V. DRAPER**
Summary. — An account is given of the various types of photography used in the feature production "Topper." Among the shots discussed are a split screen against a projected background, demonstrating the feasibility of such treatment. Other ef- fects are: multiple exposures, animated split screen, animated travelling mattes, straight animation, intricate matching of action, and a new process of subtractive matting.
A statement is included on the precautions taken to eliminate weave between the production shots taken with Mitchell cameras and the duping, which was done on Bell & Howell machines. The paper is illustrated with various selections from the picture, made by the processes described.
The reel witnessed at the Washington Convention of the Society on April 26, 1938, contained shots from the Hal Roach production Topper that are representative of the various types of trick photog- raphy used in the picture. They consist mainly of multiple expo- sures, animated split screen, animated travelling mattes, straight ani- mation, intricate matching of action, and subtractive matting.
Most of the shots, particularly where the characters appear or dis- appear, are dupes made in contact on an optical printer with hard mattes in the optical head. The general procedure on the set was to take as much of the empty set as was needed, either before the scene was started or after it was finished, depending, of course, -upon which end of the scene the split screen was to be used.
The camera was allowed to dolly or pan either before or after the part of the action requiring the split screen . At no time was the camera anchored. Of course, extreme care was taken not to move the camera while the portions of the scenes were being shot in which a character was to appear or disappear.
In most instances the action was taken on the set exactly as if
* Presented at the 1938 Spring Meeting at Washington, D. C. ; received Nov. 11, 1938.
** Hal Roach Studios, Culver City, Calif.
60
PHOTOGRAPHIC EFFECTS IN "TOPPER" 61
there were no split screen involved. The invisible actor either oc- cupied the position in which he would ultimately appear, or if the visible actor's action carried him too close to or past the spot, the in- visible one would run in and occupy his position as soon as the visible actor was sufficiently clear of his position. The invisible actor would then be cut out on a dupe and blank set substituted in his position until time for him to appear.
The last three scenes in the reel shown at Washington — of the two materializing in the car seat, Miss Bennett materializing on the bed, and the background shot driving down Broadway — for various rea- sons were discarded, but were inserted in this reel to illustrate further what can be done by the simple treatment previously described.
It will be seen from the preceding that there was nothing particu- larly new in Topper. It was made, we might say, by doing what had to be done by the best available system known to the operators in charge. It is almost safe to say that, with what is now known about what can be done in the handling of film, there is a way of solving any problem if the result justifies the effort. The text describing the various scenes accompanies the appropriate illustrations on the following pages.
62
R. SEA WRIGHT AND W. V. DRAPER [J. S. M. P. E.
The first scene on the reel (Fig. 1), in which Constance Bennett and Gary Grant ma- terialize on a log, is a combina- tion split screen and lap dissolve. After Roland Young's action carried him to the left half of the set, the screen was split optically and a straight shot of the background substituted in the right half until such time as it took for Miss Bennett and Mr. Grant to enter and take their places. The matte was then dissolved out and the original scene dissolved in.
FIG. 1.
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PHOTOGRAPHIC EFFECTS IN "TOPPER'
63
The scene showing Mr. Grant disappearing as he approaches the automobile (Fig. 2) is a lap dissolve from the scene showing him walking away into the set. The door of the car was then opened by an operator inside the car. The changing of the tire (the scene following that shown in Fig. 2) involved various types of animation, manipulating wires and concealed operators. For instance, the jack was manipu- lated by an operator in a pit under the car and the car let down by another operator.
FIG. 2.
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R. SEAWRIGHT AND W. V. DRAPER [j. s. M. P. E.
The scene in which Constance Bennett "zips" herself out (Fig. 3) was projected and mattes animated to follow the action of her hand. Miss Bennett got up and ran off the set as soon as her action was finished and Mr. Young held his position until she was clear. The length of film necessary to get her off the set was then cut out, and by use of the animated matte, plain background was made to re- place Miss Bennett as the "zipping" action progressed.
The shot at the elevator where Miss Bennett and Mr. Grant disappear while holding up Mr. Young, was a simple lap dissolve. After they had decided that they should dis- appear, they held their position for a sufficient footage to cover the dissolve, then releasing Young, they ran off the set while Young continued with his action of swaying back and forth. The scene was then dis- solved as they faded away, shortening the amount of foot- age it took them to run out of the scene. Young's action matched up and he was dissolved back in again.
FIG. 3.
Jan., 1939]
PHOTOGRAPHIC EFFECTS IN "TOPPER"
65
The shot of Miss Bennett with the vase of flowers (Fig. 4) was a split screen, lap dissolve, and wire shot. Young played the scene alone until after the box on the desk had been moved with wires, after which Miss Bennett entered the scene and, taking her position on the corner of the desk, lifted the vase. An operator watched the action through an anchored still cam- era, following the action of the vase and marking it on the ground-glass. The set was then cleared and from the same set-up the vase was lifted with wires as closely as possible in the path and at the same speed as Miss Bennett had lifted the vase. What discrepancy there was between the two actions of the vase was corrected optically on the lavender positive print and a split screen dupe made imme- diately in front of Young in which the clear set with the vase on wires was substituted until the vase started up at which time the set was dissolved out and Miss Bennett dissolved
FIG. 4.
66
R. SEA WRIGHT AND W. V. DRAPER
The bit of feminine apparel walking by itself without visible means of support (Fig. 5) was photographed against black vel- vet on a girl wearing a black velvet suit. The shooting con- tinued up to the point where they were snatched off and put into the background by a rather involved process known as subtractive matting, in which the whole of a developed and fixed print is converted back to silver bromide and re-sensitized, after which the background printed into the heavy deposit of silver representing the black velvet. Snatching the pants off was a case of matched action. In one take — that is, in the one in which the pants walked — Roland Young snatched at them in an empty set. From the same position he snatched a real pair from a wire — and the scenes were cut in action.
FIG. 5.
I
_^~- I ^ g
Perhaps the most daring shot from a standpoint of braving possible technical troubles was the shot of Miss Bennett mate- rializing in the roadster (Fig. 6). This was a split screen shot against a projection background. Actually no difficulties were ex- perienced as precautions were taken to prevent them. The Mitchell camera taking the shot was, of course, equipped with precision pins. The lavender positives were printed tails first, on a Bell & Howell printer which uses the same perforations for registry as the Mitchell. A special shuttle was built for the optical printer registering pins at the bottom, so that through- out the whole process, the same perforations were used for regis- trv.
FIG. 6.
The pen writing by itself (Fig. 7) in the close shot was straight animation. The pen was equipped with a pin in the point which was stuck into the blotter holding the pen upright as the animation progressed. The long shot was done with wires.
FIG. 7.
FIG. 8.
The shower-bath sequence (Fig. 8) was a composite of four shots. Efforts to photograph a person in a black suit under a shower proved surprisingly un- convincing. The effect finally was achieved by playing several jets of air against the water in front of a black velvet drop. The steam and the action of the soap were also taken against black velvet and the three shots doubled in over the shower-bath set. The fixtures were worked from the opposite side of the partition. Miss Bennett's ma- terialization after the shower was a simple split screen and lap dissolve.
The following shot, however, in which she snuffs her cigarette out after she has dematerialized (Fig. 9) came dangerously near to being complicated. She was dematerialized in a split screen- lap dissolve, substituting the empty set in her half until she had time to run out of the original scene. The position of her cigarette which had been located on a still camera ground- glass, was matched and the cigarette carried down to the tray with wires. This bit of action then had to be substituted for the empty set. The last puff of smoke was then shot coming through a hole in black velvet and doubled in where Miss Bennett's face was last seen.
FIG. 9.
PHOTOGRAPHIC EFFECTS IN "TOPPER'
69
The scene in which Grant materializes back of Eugene Pallette's arm (Fig. 10) de- pended more upon acting for its success than upon trick photog- raphy. Pallette struck his posi- tion in the alcove and held it without moving while Grant ran in and took his place behind Pallette's arm. After allowing sufficient footage for the transi- tion, they both picked up the action and continued the scene. In the dupe it was only neces- sary to shorten the scene with a lap dissolve the amount of foot- age it took Grant to get to his place.
FIG. 10.
70
R. SEA WRIGHT AND W. V. DRAPER
[J. S. M. P. E.
The scene in the cafe where both Miss Bennett and Grant disappear (Fig. 11) is what tech- nically is known as a "head- ache," the necessity of keeping the background action consistent being the principal problem. In this scene, which was a double split screen-lap dissolve, instead of dissolving the characters into an empty background, they had to be replaced by people, many of them moving. Perhaps it should be said that the shot was made by the "perseverance" method.
FIG. 11.
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PHOTOGRAPHIC EFFECTS IN "TOPPER"
71
The stairway scene (Fig. 12) was made by the same method with slight variations. It may have been noticed that Young crossed to Grant's side of the screen the moment Grant dis- appeared. From the techni- cian's standpoint it was a mo- ment too soon, for Mr. Grant had not yet run off the set. As a consequence, it was neces- sary to animate the split screen matte which had been intro- duced to dissolve Grant out of the scene ahead of Young as he advanced, and re-animate the opposite matte which printed in the plain background without losing that almost imaginary line that makes a perfectly blended match.
FIG. 12.
72
R. SB A WRIGHT AND W. V. DRAPER
Grant's sitting on the chande- lier (Fig. 13) was a split screen- lap dissolve. The only diffi- culty was that the closeness of the actors below necessitated a very sharp blend and an un- usually shaped matte.
FIG. 13.
LATENT IMAGE THEORY AND ITS EXPERIMENTAL APPLICATION TO MOTION PICTURE SOUND- FILM EMULSION*
W. J. ALBERSHEIM**
Summary. — In a previous paper the writer attempted to show that the latent photo- graphic image is formed in two distinct and separate steps. In the present paper this, theory is compared with recent physical research. The writer concludes that each of the photographic steps consists of the attraction of one electropositive silver ion to a sensitizing speck on the grain surface which has previously captured an electron.
The reciprocity law failure at high intensities is explained by the minimum time re- quired for the attraction of a silver ion. The reciprocity law failure at low intensities is explained by assuming that a sensitizing speck which has attracted only one silver ion is unstable and that the number of grains activated by a single capture decreases exponentially with time.
From these physical theories the writer deduces mathematical relations governing the photographic characteristics. H&D curves and reciprocity failure curves com- puted from these relations are in good qualitative agreement with experimental curves.
The assumption of an unstable intermediate state of insufficiently exposed grains implies certain effects of delayed fogging and delayed development which are verified by experiments.
In a previous paper1 by the writer, it was deduced from the shape of the photographic H&D curves that a grain of motion picture film must be hit by at least two photons in order to become developable. At that time, no physical explanation of this "double hit" theory was attempted and hope was expressed that the theory would be supplied by research physicists.
There is, of course, no lack of research nor of physical theories in this field. On the contary, one is overwhelmed by an ever-increasing wealth of literature ; in fact, the writer's attention was called to some important contributions after completion of the analytical studies which form the basis of the present report.
Unfortunately, the various investigators do not agree even in some of the most fundamental assumptions. While most of them assume
* Presented at the 1938 Spring Meeting at Washington, D. C. ** Electrical Research Products, Inc., New York, N. Y.
73
74 W. J. ALBERSHEIM [j. s. M. P. E.
that the latent image consists of silver atoms, recent work carried out in the Eastman-Kodak Research Laboratories2 suggests that the solarized image alone forms a metallic silver cluster which is amenable to chemical-physical development only, whereas the latent image, being subject to chemical development, must be differently constituted. A further divergence of opinion exists with regard to the number of photons required for latent image formation. Some of the earlier research3 showed that in single halide crystals the ratio of metal atoms reduced by light to the number of absorbed photons, i. e., the photochemical quantum -efficiency lies between one-quarter and one. Other workers stated4 that a film grain in a photographic emulsion must absorb about 100 quanta in order to become develop- able, whereas a recent series of tests5 proved that for various negative and positive emulsions the number of quanta incident upon an average sized photographic grain needed for formation of a latent image is of the order of 50. Since the grains are transparent and absorb only a fraction of the incident photons, their photographic quantum-effi- ciency must be considerably greater than l/w.
We begin our survey of experimental knowledge with the photo- graphic toe characteristic. As shown in the previous paper,1 the shape of the characteristic curve requires for the activation of the film grain by light, two separate physical steps which were mathe- matically represented in that paper by differential equations 49 and 72. It must be understood, however, that these two steps are not necessarily to be identified with two single photons of light. They only mean two processes initiated by illumination in which the oc- currence of the second process depends upon the completion of the first, so that the probability (or average quantum-efficiency) for the formation of a latent image by a photon is the product of the separate probabilities for the two steps taken singly. The absolute number of photons required for the completion of each step affects the photo- graphic inertia rather than the toe shape of the characteristic which depends only on the ratio between the 2 efficiencies. This toe shape at low exposures is difficult to analyze from ordinary logarithmic H&D curves. It has been investigated by many authors but, in most cases, with sources of illumination quite different from visible light.
Silberstein and Trivelli6 as well as Jauncey and Richardson7 found that the density of the developed photographic image originating from weak x-ray exposures grows in linear proportion to exposure.
Jan., 1939] LATENT IMAGE THEORY 75
Silberstein and Trivelli also proved that the number of developable photographic grains is equal to the number of photons impinging upon the grain surface. For these x-rays therefore a "single step" theory is established. However, x-ray photons have an energy con- tent which is many thousand times greater than that of the visible light photons used in sound recording. Since a double step process is claimed for visible light, there must be an intermediate range of wavelengths at which a transition from the single to the double step occurs. This seems to be actually the case :
FIG. 1. Characteristics of film exposed to x-rays and between double intensifying screens.
Hirsh8 showed that, although in images formed by hard x-rays the density increases proportionally to irradiation, the density-exposure characteristic begins to curve upward when the x-rays are softened to a wavelength of over six Angstrom units.
This curvature means that the probability of latent image forma- tion is proportional to a power greater than one of irradiation so that on the average more than one photon per grain is needed for the latent image formation.
In order to free the comparison between x-rays and light from the influence of the types of emulsion used, the writer asked the Eastman Kodak Laboratories to supply information regarding the different photographic characteristics of one and the same emulsion when
76
W. J. ALBERSHEIM
[J. S. M. P. E.
exposed to x-rays and to visible light. Mr. Wilsey of the Eastman Kodak Physics Department very kindly supplied the characteristics which are shown in Fig. 1 of this paper. Curve A of this figure is produced by x-ray exposure and shows a long sloping toe which in the previous paper1 was shown to correspond to the "single hit" theory and incidentally to high transparencies of the emulsion. Curve B is obtained by exposing the same film between double intensifying screens. These intensifying screens are fluorescent surfaces which emit a great number of visible light photons when hit by a single x-ray photon. As stated by Mr. Wilsey "when the exposure is made with intensifying screens, practically the whole photographic effect is due to the fluorescent light from the screens so that the H&D response
PAR SPEED PORTRAIT FILM
DENSITY -i
1.2 18 QA
L06 INTENSITY
FIG. 2. Constant-density curves for different development times. A — 5 minutes' development, B — 30 minutes' development.
is essentially that due to exposure to light on both sides of the film." It is evident that the toe of Curve B shows a much greater sharpness than that of Curve A corresponding to an exponent greater than one and therefore consistent with the double hit theory. (A three-step process can not play any important part in sound-film emulsions be- cause it would cause a toe-curvature greater than that found under actual conditions.)
If one accepts the two separate steps of exposure as a fact, what are the known properties and time requirements assignable to these steps ? This information may be derived from a comprehensive series of tests conducted chiefly by Jones, Webb, and other physicists of the Eastman Kodak Laboratories on the subjects of "Reciprocity Law Failure" and "Intermittency Effect," which are closely linked to each other. The main features of the reciprocity failure effect
Jan., 1939]
LATENT IMAGE THEORY
77
may be illustrated by our Fig. 2 which is a reproduction of Fig. 9 of a paper by Jones and Hall published in 1929.9 In this figure the logarithm of exposures required to produce given densities is plotted against the logarithm of intensity. The reciprocity law assumed that the photographic effect depended only on the total number of photons impinging on the film grain ; that is, on the total exposure. If this were true the curves of Fig. 2 should be horizontal lines. Actually, the lines "fail" to be horizontal and curve upward at very low and very high intensities. Kron and Halm10 re- ported that this curvature can be approximated by a catenary rela- tionship, which in Fig. 2 is illustrated by solid lines. However, at the left side of this figure one sees dashed lines breaking away from
Ea&imao Slow Lantern P1a4es
3.9 45 It 3.7 2.3 2.9 1.5 at 0.1 1.3 19 2.5 3.1 LOG, INTENSITY
FIG. 3. Constant-density curves for slow emulsion showing low- intensity departure from catenary equation. Top curve, density = 4.2; bottom curve, density = 0.20.
the catenary and rising at an angle of about 45° which limits the curve fitting range of the catenary and deprives it of physical significance. Another series of such curves is shown in Fig. 3 which is a reprint of Fig. 11 of the above-mentioned paper. In these figures, the logarithm of intensity is used as abscissa axis in accordance with historical precedent. This historical usage seems to the writer to be an un- fortunate choice which has for a long time beclouded the underlying physical relations. When one talks of a greater intensity in a physical process, such as a baseball hit, one thinks of greater speed or greater muscle tension. But when one talks of intensity of illumination with light of a given color, all the little baseballs, that is, the photons of light, hit their objective with the same speed and with the same energy of impact. What is meant by "intensity of illumination" is actually the number of photons per second, and denotes a quantity
78 W. J. ALBERSHEIM [j. s. M. P. E.
rather than a quality. The physical dimension of this "intensity" is energy times sec."1. Since the scale is logarithmic, it is only necessary to reverse the sides of the diagram in order to plot as abscissa axis the logarithm of the reciprocal factor; that is, of the average time interval between successive photon impacts upon a film grain.
This slight difference in the interpretation of the abscissa axis might have greatly speeded up the progress of research, for the im- pact time interval has recently been shown by J. H. Webb5 to be a most important factor in the reciprocity law failure effect. In his investigation of the relation between reciprocity failure and the in- termittency effect, Webb discovered that intermittent exposures are equivalent to continued exposures with an equal total number of photons radiated and equal total duration, provided that the interrup- tion cycle is completed within the average time interval between successive photon impacts upon one and the same grain surface.
Webb defines reciprocity law failure as the effect produced by the tune distribution of quanta reception by a photographic grain (in agreement with our double step theory) .
This theory accounts for the reduced efficiency at both extremes of intensity, or rather of exposure time in the following way : Reciproc- ity failure at high intensities means that the first step requires for its completion a small but definite average time interval, before the second step can take place: If a new photon hit, or group of hits, occurs before the "step," i.e., the physical process initiated by the previous photon hit (or hits) has had time to be completed, the additional hits just "do not count" and very short exposures can not utilize all received light quanta for the production of developable photographic grains.
Disregarding for simplicity's sake the statistical variations in the time requirements of the first step, we note for incorporation into our mathematical picture, that the effective time interval between successive photon impacts upon a film grain exceeds the actual time interval by a fixed minimum time which hereafter is called the "blocking time."
In order to account for the reduced efficiency of the photographic process at very low intensities, that is, very long exposure times, it is necessary to make an additional assumption: The configuration produced by the first step of latent image formation must be elec- trically or chemically unstable , a stable latent image being only ob- tained by the completion of the second step. The simplest form of
Jan., 1939] LATENT IMAGE THEORY 79
this assumption is that grains activated by completion of the first step fade back to the unexposed state according to an exponential time func- tion, as if the activated grains were a radioactive substance re-emitting the stored light energy in random manner. Some of this released energy may be detectable by photographic or other methods. The time after completion of exposure in which the number of activated grains is reduced by a factor e will be introduced into our equations as the "fading time."
However, before attempting the mathematical analysis of this de- layed step-by-step mechanism, an attempt should be made to find a plausible physical explanation for the somewhat involved process of image formation which we deduced from two such well established every-day characteristics as the H&D curve and the reciprocity failure curve!
As previously mentioned, the research of Przibram, Smakula, Hilsch, and Pohl3 shows that in single silver halide crystals the photo- chemical action consists of a liberation of silver atoms from their crystal bonds to the halide ions, the number of atoms thus reduced being proportional to the number of photons absorbed. This sug- gests that the two photographic steps are related to the number of deposited silver atoms rather than to the number of incident photons. This interpretation is made more probable by the above-mentioned fact that one and the same emulsion has entirely different character- istics when exposed to x-rays and to visible light. The powerful x-ray photons blast the required number of silver atoms out of the halide crystal in a single hit, whereas the weaker light photons can only dis- place them one at a time. The double step hypothesis is thus nar- rowed down to a "double atom" hypothesis. It implies two claims which must be substantiated : (a) That in spite of the low quantum efficiency of grain exposure, two silver atoms deposited at the right place are necessary and sufficient to make a photographic grain de- velopable; and (b) that the deposition of these two atoms proceeds in separate steps.
Considerable light is shed upon the minimum size of development nuclei by the research of W. Reinders and his associates.11 These investigators condensed extremely thin films of silver on glass plates and developed them in solutions containing a mixture of chemical developing agents and free silver salts. The minimum developable silver density turned out to be 1/5ooth of that corresponding to a single atomic layer. The authors assumed that the deposited silver atoms
80 W. J. ALBERSHEIM Q. s. M. P. E.
combine into groups if they are condensed within a mutual distance, no larger than that vvhich separates them in a metallic silver crystal, and they computed the probability of various group sizes. The ob- served minimum density was found just sufficient to permit the oc- currence of four-atom groups. Hence it was concluded that aggre- gates of four or more silver atoms can serve as nuclei of development.
It has been well established by the work of Sheppard and others12 that development starts at so-called sensitizing specks which seem to consist of silver sulfide molecules. Reinders found that sulfide molecules can act as centers of development just as well as silver atoms. Reinders and his associates then applied their probability calculus of group formation to the amount of silver sulfide present in photographic emulsions. They found that according to Shep- pard's reports there are several hundred silver sulfide molecules avail- able for each grain; that each grain is likely to have on its surface (and perhaps in its interior) several groups consisting of two sulfide molecules each; but that on only a small percentage of grains (less than 10 per cent) aggregates of three sulfide molecules will be formed. Now one may "put two and two together:" If two units of aggrega- tion are supplied by the sulfide molecules of the sensitizing specks and if aggregates of four are needed to make a grain developable, it is evident that two additional units must be supplied by the photo- graphic process in the form of silver atoms or silver ions.
The manner in which the silver atoms find their way to the sensitiz- ing specks is explained by J. H. Webb13 and by Gurney and Mott.14 According to quantum mechanics the primary action of the photon consists in knocking loose an electron from its attachment to a halide ion. If the electron receives sufficient kinetic energy it can travel freely through the previously insulating halide crystal as if the crystal were a metal. These electrons are "captured" at regions of the crystals in which the electrical potential is more positive than average. Such trapping points may consist of small fissures and ir- regularities in the crystal or, more likely, of impurities, such as the silver sulfide molecules of the sensitizing specks, which will be charged up to a higher negative potential by the captured electron.
Gurney and Mott suggest that at normal temperatures the thermal agitation will throw some silver atoms out of their normal positions in the crystal lattice, producing slightly mobile negative "holes" and and highly mobile positive silver ions. The free silver ions are elec- trostatically attracted by the electrons captured at the sensitizing
Jan., 1939] LATENT IMAGE THEORY 81
specks and move toward them like the ions in a liquid electrolyte. This description fits very nicely into our step-by-step pattern. The union, or at least close association, of a silver ion and an electron completes one photographic step by neutralizing the free charges. Since the net motion of the silver ion in the electrostatic field of an electron is relatively slow, it becomes plausible that the completion of this photographic step takes a measurable amount of time. Before neutralization of the charges the negative potential of the captured electron repels any further electrons which might be liberated by light and prevents them from reaching the same sensitizing speck. This, as discussed above, accounts for the reciprocity failure at high intensities.
After completion of the first step the silver ion is not fully stabilized at the sensitizing speck. Due to thermal agitation there exists during each time interval a small probability that the electron which at- tracted it is thrown off or "evaporated." In that case the electron begins to travel freely through the crystal and is either captured by another sensitizing speck or by a crystal irregularity, or it may re- combine with the positive electron hole created when it was first knocked out of the crystal by the impact of the photon. This leaves a single silver ion unattached and it in turn resumes a random thermal motion through the crystal, probably being recaptured by a negative hole in the lattice. If, however, two steps are completed, that is, two silver ions and their electron mates are united at the sensitizing speck, they presumably form a silver molecule which is more stable than a single silver atom and much less likely to give up an electron by heat evaporation. By assigning silver atoms to the small nuclei of chemical development this mechanism 'differs from the view of Evans and Hanson2 who attribute metallic nature only to the solarized nucleus. Possibly the discrepancy can be solved by assuming that in small nuclei containing very few silver atoms, these atoms remain closely embedded in the crystal structure so that chemical development can spread out from the sensitizing speck into the crystal. When the number of silver atoms grows due to over- exposure, they exert an increasing mechanical pressure upon the sur- rounding crystal. Finally this pressure will tear the silver cluster loose from the silver halide. The cluster can be physically developed by silver deposition but it is physically and chemically divorced from the halide crystal which reverts to the "unexposed" state minus a sensitizing speck.
82
W. J. ALBERHSEIM
[J. S. M. P. E.
The above physical interpretation follows closely the viewpoint of Gurney and Mott and differs from it mainly by assuming that the deposition of two silver atoms suffices to make a grain developable, whereas the said authors imply that a greater number is necessary. If two atoms only are required and if a single photon has sufficient energy to liberate an atom, why is it that on the average dozens and in some emulsions even hundreds of photon impacts strike a grain surface before it becomes developable ? The reason may be found in a relatively great number of sensitizing specks per film grain. Assume, for instance, that the grain contains ten sensitizing specks of which
FIG. 4.
Showing the reduction of photographic efficiency produced by an increase in the intensity of light.
nine are located in the inaccessible interior of the grain and only one on the surface where it can be reached by the developer. Even if there were no other trapping possibilities but the sensitizing specks, the probability for a liberated silver ion to reach a sensitizing speck on the surface of the grain would be only Vioth. The probability of a second silver ion's reaching the accessible sensitizing speck pre- viously reached by the first ion would also be Vioth, so that the com- bined probability for the formation of a developable grain would be Viooth for two photon impacts, or 1/2ooth per photon.
The above-described mechanism accounts for the known experi- mental facts in a qualitative manner. As a next measure, therefore, it was brought into a simplified mathematical form. The differential
Jan., 1939]
LATENT IMAGE THEORY
83
equations governing the two steps and their solutions are given in the mathematical appendix attached to this paper. The equations differ from the double hit equations of the previous paper1 by the blocking time required between the first and second step and by the gradual decay of film grains in which the first step only was com- pleted. At the limit of zero blocking time and infinite decay time which is approached for medium intensity, the new equations coincide with the old ones. The H&D curve at this medium intensity has been plotted as the extreme condition in the curves of Figs. 4 and 5. Fig. 4 shows the reduction of photographic efficiency produced by
FIG. 5. Computed H&D curves for long exposure times at decreas- ing intensities.
an increase in the intensity of light. At extremely high intensity levels shown at the right side of Fig 4, the shape of the H&D curves approaches that of the x-ray characteristic, Curve A, in Fig 1. One reason for this is that the efficiency is at a minimum at the front sur- face of the emulsion where the excess of photons is greatest so that there is little difference between the photographic effect in front and rear of the emulsion : the effective penetration increases. Further- more, due to the abundant supply of freed electrons a second electron will reach every sensitizing speck and initiate the second step im- mediately after completion of the first step. This makes the photo- graphic process a function of the first step only, i. e., the equivalent of a single-step process. The time-scale gamma increases with intensity
84
W. J. ALBERSHEIM
[J. S. M. P. E.
due to the high penetrating power, and the straight-line portion of the H&D curve is shortened.
In Fig. 5, a similar series of H&D curves has been computed for long exposure times at decreasing intensities. The photographic effect falls off first at the rear of the emulsion where a long time in- terval between successive photon impacts allows the end products of the first step to fade away before a second photon is received. Con- sequently, the effective penetrating power decreases, producing at extremely low intensities a reduced gamma and a straight-line portion of the H&D curve extending high up toward the shoulder. Whether this idealized relation is followed under practical conditions may be
LOG X LOG RELATIVE MTCNSITY
FIG. 6. Constant density curves, computed: "reciprocity failure."
doubted. The great effective absorption requires extreme exposures in the front of the emulsion to obtain a reasonable overall density and this may lead to solarization and loss of density in the shoulder region.
All characteristics of Figs. 5 and 6 are "time-scale" curves. The intensity-scale curves deviate increasingly from these for the more extreme exposure ranges: As shown in the Appendix, the ratio of time-scale gamma to intensity-scale gamma is a function of the slope of the reciprocity failure curve.
By picking points of equal density on the various curves of Figs. 5 and 6 and plotting their exposure logarithm as function of the in- tensity logarithm, one obtains "reciprocity failure curves" as shown in Fig. 6. Comparing these curves with the experimental curves of Figs. 2 and 3, one notes the similar character although the rise of
Jan., 1939]
LATENT IMAGE THEORY
85
the computed constant density curves at the high and low ends is somewhat too sudden. The shape of the measured reciprocity failure curves can be explained by considering that actual film emulsions do not have grains of uniform size and composition as assumed in our simplified calculations, but that they consist of a wide range of grain sizes containing different numbers of sensitizing specks. In a smaller grain it will, on the average, take less time for the silver ion to reach the electrified sensitizing speck, hence its blocking time is shorter. On the other hand, the statistical fluctuations are smaller in a smaller grain, thus reducing the probability for electrons to evaporate from the sensitizing speck and increasing the decay time.
*i*
FIG. 7. Constant density curves, computed : "reciprocity failure. "
Hence, actual reciprocity failure curves will be produced by the super- position of a great number of contributing curves which are trans- posed laterally. There will therefore be on each side of the curves an intermediate range of reduced and fairly constant slope, depending upon the statistical distribution of grain sizes.
In Fig. 6, lines of equal exposure time have been drawn, in the form of thin straight lines rising at an angle of 45 degrees toward the right in a manner which seems to have first been used by Jones and Webb.15 Since the reciprocity failure is determined by two time constants, namely, the blocking time and the decay time, it would be more instructive to plot the logarithm of the total irradiation (It) as a function of log T rather than of log /. This has been done on
86
W. J. ALBERSHEIM
[J. S. M. P. E.
Fig. 7. It is seen that the photographic process is completely ineffi- cient at exposure times shorter than the blocking time. At somewhat longer exposure times the required irradiation reaches a minimum, and at extremely long exposure times, exceeding the decay time, the required irradiation for constant densities increases with the square root of exposure time.
Having thus verified that even in its simplified mathematical form the two-step theory fits the facts that led to its adoption, we con- sidered it necessary to put it to an experimental test by checking new
A: AT" contrast without fogging.
B: 2AE.
C: AE-1000 cycle single amplitude.
D: JEj-D.C. component of signal.
G: E2-Foggmg.
H: AT" contrast with fogging.
/: Ei + £2.
FIG. 8. Increase of contrast by fogging.
facts which can be predicted from it. The most significant of these facts seems to be connected with the claimed instability of the activa- tion produced by the first photographic step. In the under-exposed toe region of the characteristic the irradiation produces relatively very few grains in which the two steps of latent image formation are completed, but a much greater number, in which one step only has taken place, that is, one silver atom transported to a sensitizing speck on the grain surface. After development these under-exposed pic- tures show negligible contrast. However, their contrast can be in- creased by superimposing to the picture a constant illumination.
Jan., 1939] LATENT IMAGE THEORY 87
This is known as "fogging," and depending on whether the super- imposed d-c. exposure takes place before or after the under-exposed modulated exposure, one speaks of "pre-fogging" and "post-fogging." The purpose and effect of fogging are illustrated by Fig. 8. According to our view, fogging can only be efficient if the time interval between the two superimposed exposures is smaller than the decay time so that the activated "single-step" grains do not have time to fade out. This theory was verified by the following "fading test": A sound- track was exposed to a thousand-cycle signal with very low intensity of illumination, E\ (Fig. 8) producing a specular density of only 0.07. Upon this weak signal exposure we superimposed a uniform fogging exposure Ez with about three times greater average light in- tensity. One part of this fogging exposure was applied ten minutes before the signal, a second part one-half hour after the signal, and
TABLE I
Fading Test
Hours between Relative Level Specular
Signal and Fogging (Db.) Density
No fogging -17.4 0.069
-0.2 0.0 0.168
+0.5 0.0 0.172
+ 1.0 - 0.05 0.164
2.0 - 0.2 0.165
4.0 - 0.5 0.160
6.0 - 0.75 0.158
21.5 - 2.1 0.142
further parts after increasing time intervals up to 21.5 hours. The result of this test is tabulated in Table I and shown on Fig. 9. It shows that fogging applied within ±0.5 hour of the signal improves the a-c. output by 17 db. and that with increased time intervals this benefit was reduced by about 0.1 db. per hour. During the test time of 21 hours, the total average density decreased from 0.17 to 0.14. This decrease in density would have increased the level by 0.6 db. if the modulation had remained constant. The actual decrease of modulation therefore amounts to about 2.7 db. Since without fog- ging the signal level was negligible, the modulation loss can only be explained by a fading of the partly exposed grains in the time in- terval between signal and fog exposures.
The change of average density, however, may have a double ex- planation : In addition to the fading effect proved by the signal loss,
W. J. ALBERSHEIM
[J. S. M. P. E.
there may exist an increase of the quantity of fully exposed grains available for development with time. Such an "intensification effect" has been mentioned in the literature. In the discussion of a paper on dry hypersensitization before this Society,16 Mr. J. I. Crabtree of the Eastman Kodak Company stated, "It is well known that you may get effective hypersensitization or growth of the latent image by merely storing the latent image." The two-step theory leads one to expect such an intensification from the following reasoning: Assume that a film grain has ten sensitizing specks and that due to an insufficient
-1.6 -
-Z
#et*rtve tevei.
8 •' artcui** Otff»trr~
0 Z 4 6 6 tO fZ 14 16 19 20 ZZ HOURS BeTHKCN 5IGWU. GHD fOSOIHS CXPOSUKE
FIG. 9. Fading test; E. K. emulsion 1359.
exposure five of these specks have received one silver atom each, but that in none of these specks the latent image has been completed by the absorption of a second silver atom. According to Gurney and Mott's theory, some of these specks will give up electrons by evapora- tion and these free electrons will move through the crystal just as if they had been liberated by an additional photon of light. There exists, therefore, a certain probability that one of these electrons will be captured by an "activated" sensitivity speck which has already received one silver atom. The capture of this additional electron and the subsequent attraction and absorption of a second silver ion will complete the second step for this grain and make it stable and
Jan., 1939]
LATENT IMAGE THEORY
developable. This process is, of course, much more likely to occur after weak exposures, when the number of partly exposed grains exceeds that of fully exposed grains. The intensification process will occur mainly in the toe region of the H&D curve. In a modulated sound-track exposed in the straight-line region of the H&D curve, the effect will be a considerable darkening of light portions and a small darkening of the darker portions, that is, a net loss of modula- tion.
This theory was put to the test in the following manner : Alternate sections of film were exposed with unmodulated light, 500-cycle
CURVE A : MODVl.»TION LOSS 6 •• DCHSITY INT
4 5 6 7 DAYS BEFOB£ D£.Y£L,OPMeNT
FIG. 10. Intensification test; E. K. emulsion 1359.
modulation and with 8000-cycle modulation, and portions of all three types of exposures were developed after storing times increasing from 1 to 13 days. The comparison of high-frequency and low-frequency signals was included because it had been suspected that some of the electrons liberated in the fading process might have sufficient energy to expose an adjacent grain and thus to produce an image diffusion recognizable as a high-frequency loss. The results of this test are given in Table II and Fig. 10. After correcting for the daily variations in development characteristics, there was an increase in the average density of the modulated as well as of the unmodulated sound- tracks amounting to about 0.01 per day and a loss of modulation amounting to about 0.35 db. per day. The small increase in the den-
90 W. J. ALBERSHEIM [j. s. M. P. E
sity of the unmodulated sound-tracks shows that the loss of modula- tion must be nearly entirely due to an intensification of the low-den- sity portions. These findings explain why the motion picture studio operators dislike recording films on the last day of the working week and storing them over the week-end before development.
TABLE II
Intensification Test
Days between Relative Modulation Average
Exposure (Dh>.) Modu- Average
and De- lation Specular
velopment 500~ 8000~ Loss (Db.) Density
1 0.0 - 0.7 0.0 0.62
5 -1.4 - 8.3 1.35 0.69
8 -2.4 - 9.4 2.4 0.71
13 -5.1 -11.8 4.95 0.725
Fortunately, the fading time of commercial emulsions at normal temperatures is so long that the photographic result is not noticeably impaired, provided development takes place within a day of exposure. For professional motion picture work, it does therefore not seem neces- sary to include the time loss of modulation due to low-density in- tensification into the analytical expressions for latent image formation which are cumbersome enough without this added complication! From the experimental point of view, however, the positive result of the fading and intensification tests has encouraged us to present the "step-by-step" or "two-atom" hypothesis as a small contribution to the comprehensive quantum theory of the photographic image formation built up by so many research workers and culminating at the present time in the work of Webb and of Gurney and Mott.
REFERENCES
1 ALBERSHEIM, W. J. : "Mathematical Relations between Grain, Background Noise, and Characteristic Curve of Sound-Film Emulsions," /. Soc. Mot. Pict. Eng.t XI (Oct., 1937), No. 4, p. 434.
2 EVANS, R. M., AND HANSON, W. T.: Phot. J. (Aug., 1937), p. 497.
3 PRZIBRAM, K.: Z. fur Physik, 20 (1923), p. 196. SMAKULA: Z.fur Physik, 59 (1929), p. 603.
HILSCH, R., AND POHL, R. W. i Z.fur Physik, 64 (1930), p. 607.
4 EGGERT, J., AND NODDACK, W.: (1932). See ref. 14, p. 156.
6 WEBB, J. H.: /. Opt. Soc. Amer., 23 (May, 1933), No. 5, p. 157. 6 SILBERSTEIN, L., AND TRiVELLi, A. P. H. : Communication No. 409, Eastman Kodak Research Lab.; Phil. Mag. (7th Ser.), 9 (1930), p. 787.
Jan., 1939] LATENT IMAGE THEORY 91
7 JAUNCEY, G. E. M., AND RICHARDSON, H. W.: /. Opt. Soc. Amer. (May, 1934), p. 125.
8 HIRSH, F. R. : /. Opt. Soc. Amer. (Aug., 1935), p. 229.
9 JONES, L. A., AND HALL, V. C.: Proceedings 7th Internal. Cong. Phot. (July, 1928).
10 KRON, E.: Pub. Astrophys. Obs. Potsdam (1913), No. 67. HALM, J. R.: Astron. Soc. Monthly Notices (June, 1922), p. 473.
11 REINDERS, W., AND HAMBURGER, L.: Z. fur Wissensch. Phot., 31 (1933), Nos. 1 and 2; Ibid., No. 10.
REINDERS, W., AND DE VRIES, R. W. P.: Z. fur Wissensch. Phot., 56 (1937), Nos. 9 and 10, p. 985.
12 SHEPPARD, S. E., TRIVELLI, A. P. H., AND LOVELAND, R. P.: J. Franklin Inst., 200 (1925), p. 51.
13 WEBB, J. H.: J. Opt. Soc. Amer., 26 (Oct., 1936), No. 10, p. 367.
14 GURNEY, R. W., AND Moxx, N. F. : Proc. Royal Soc., 164A (Jan., 1938), p. 151.
15 JONES, L. A., AND WEBB, J. H.: "Reciprocity Law Failure in Photo- graphic Exposure," /. Soc. Mot. Pict. Eng., XXIII (Sept., 1934), No. 3, p. 142.
16 DERSCH, F., AND DURR, H.: "A New Method for the Dry Hypersensitiza- tion of Photographic Emulsions," /. Soc. Mot. Pict. Eng., XXVIII (Feb., 1937), No. 2, p. 186.
ANALYTICAL APPENDIX COMPUTATION OF PHOTOGRAPHIC CHARACTERISTICS
(1) Physical assumptions and definitions
(1.1) A latent image is formed by the deposition of two or more silver ions at a sensitizing speck located on the grain surface and ac- cessible to the developing agent. A grain in which this image forma- tion is completed is called "exposed."
(1.2) Silver ions are transported to the sensitizing specks by the electrostatic attraction of electrons liberated by photons from the halide crystal and trapped by the sensitizing speck; this transporta- tion takes a measurable average time called the "blocking time," tb. The union of silver ion and electron neutralizes the free electron charge and completes a photographic "step."
(1.5) Before completion of the photographic step the electron charge repels any further electrons and prevents them from being trapped by the same sensitizing speck.
(1.4) A grain in which only one photographic step is completed, is in an unstable "activated" state. An electron and subsequently the silver ion attracted by it may be lost by thermal agitation. The time constant of this loss, i. e., the time in which the number of acti- vated grains is reduced by the factor e, is called the "fading time," 7}.
92 W. J. ALBERSHEIM [j. s. M. P. E.
(1.5) An "exposed" grain per 1.1, is stable and remains developable. (The fact that an excessive amount of deposited silver atoms may "solarize" the grain and make it inert to chemical development, is of no importance in the exposure range of motion picture sound-films.)
(1.6) The grains are distributed at random throughout the photo- graphic emulsion.
(1.7) Due to absorption the light intensity decreases nearly ex- ponentially with depth of penetration. The absorption constant n is defined as the reciprocal of the depth at which the number of photons per second is decreased by the factor e.
(1 .8) Effective Electron Time Interval. — The average time interval be- tween photon impacts on the grain may be called TP. The absorp- tion factor of single grains for photons is called pa. The probability that an electron is liberated by the absorbed photon, is called pe. The probability that a liberated electron penetrates to an unexposed, accessible sensitizing speck is called pffl. The probability that a liberated electron penetrates to an activated accessible sensitizing speck, is called pgz.
One finds the effective time interval between photo-electrons ar- riving at an unexposed speck :
(1}
and the effective time interval between photo-electrons arriving at an activated speck
CTi W
(1.9) Additional Symbols (See list of symbols at the end of ap- pendix).— In order to maintain a connection with the previous paper1 we define g as the fraction of the grains at a given depth in the emul- sion which has been activated but not fully exposed, and r as the fully exposed fraction. Where convenient, we use the fading factor:
/ = i w
and the intensity factor:
Jan., 1939] LATENT IMAGE THEORY 93
(2) Differential equations for the steps of latent image formation
(2.1) Equation for the First Step. — The gross increase of activated grains is proportional to the available number of unexposed grains and to the intensity factor. From this gross increase one must deduct the decrease due to fading and the decrease due to a transformation of activated grains into fully exposed grains. Hence:
dt Ti Tf dt
or g' = (1 - r - f) i - fg - r' (6)
(2.2) Equation for the Second Step. — The increase of exposed grains is proportional to the available number of activated grains, divided by the effective electron time interval plus the blocking time :
Hence g = r' (tz + tb) (8)
and g' = r" (t2 + tb) (9)
(2.3) Solution for a Single Emulsion Layer. — Introducing the values of 8 and 9 into 6 one finds :
r + Ur' + Vr" = 1 (10)
with U = Ti + (h + tb)(l + fTi) (11)
and V = (tt + tb)Ti (12)
A solution of 10 must have the form:
r = 1 + ri-kit + rt-k*t (13)
At / = 0, both r and g and, in view of (7), r' must equal zero. Hence 13 can be transformed into:
ri + r2 + 1 = 0 (14)
riki + r2k2 = 0 (15)
from this one finds :
r, = r^-r (16)
k\ — K2
r 2 - - ^ (17)
and r = 1 + _A_e-^ ***-**
94 W. J. ALBERSHEIM [j. s. M. P. E.
From 10 one finds for ki and kz the relation:
rlf-kit (i _ Uki + W) + r2€-*rf(l - Ufa + VW} = 0 (19) from which it follows that :
1 - Uki + VkS = 1 - Ukt + VW = 0 (20}
I (21}
General Equation of H&D Curve. — Equations 18 and 21 de- scribe the formation of the latent image at uniform intensity, and therefore at one given depth in the emulsion. The itensity itself de- creases exponentially with depth :
iv = ioe~uy (22}
r< = I = Tioe»v (23}
Tz = C Ti = 5 = T2oe"« (24}
If R is defined as the fraction of all grains in the emulsion which has become developable, one sees that after uniform development :
R = D/Dm (25}
where D is the measured density and D^, the highest density obtain- able with the same emulsion and development. According to defini- tion, R is found as :
^ r
Y I
Jo
'y r dy (26}
in which dy denotes a differential emulsion layer and Y the total emulsion thickness. In view of 22:
dy = -^ (27}
*--4 ftr£- _4_ f*«« w
in which r is the transparency of the emulsion for the photographically active light. In order to make more clear which factors of 21 are functions of i, it may be transformed into :
Jan., 1939] LATENT IMAGE THEORY 95
Combining IS, 25, and 28, one finds:
D = - .£ ' 1-+ *L_ .-I- - *L- .-*- d4 (30}
- .£ f '(
lnrJiQT \
Equations 29 and 30 constitute the general solution for the H&D curve as function of the light intensity at the surface and the length of exposure, assuming, however, that all grains are uniform in size and constitution.
(2.5) Evaluation of H&D Characteristics. — If one introduces the full values of k from 29 into 30, the integral becomes very compli- cated and unmanageable for computation. It can, however, be sim- plified by the following considerations :
The constant C in equations 2 and 29 denotes the decrease in prob- ability of electron capture by the presence at a sensitizing speck of one or more silver ions and electrons which neutralize each other's charges. The additional silver atoms may lower the work function and thus increase the probability of capture so that C would be some- what smaller than one. However, its magnitude will not differ much from unity and its effect will be about equivalent to a mere change of film speed. C will therefore be considered equal to one in the follow- ing computations.
Furthermore, blocking time and fading time are of very different orders of magnitude : The blocking time is measured in microseconds, the fading time in hours. One can therefore regard the one as zero or the other as infinite, according to the intensity range explored. This splits the computation into a high-intensity and a low-intensity range.
(2.51) Computation of High-Intensity Curves. — Equation 29 is sim- plified into :
(31}
Introducing the new variable :
tbi = x one finds: (32)
ky = 0.5*
+ x I + x
= i (34}
—L- (55)
1 + x
96 W. J. ALBERSHEIM [j. s. M. P. E.
*yi + * _ i
* - *yi +
(36)
^
- 1 + x i * ( Q7\
i _ in + * - -5- ~ *
Introducing the variable :
t/tb = z one finds: (38)
X \ X
In view of 32
-= and
x ^
(42)
xz = it = e (43)
(2.511) Approximate Solution at Relatively Low Intensities. — At low intensities
lim x > 0 (44)
The integral of 42 can be rewritten :
x*€ L *J
For small x values this approaches :
For a given exposure time :
™ = ™ = ^ hence (47)
x i e
= 1 + JL Ce e-e (l+e)?Z and
-fct J> -•-'?.
Equation 45 is identical with equation 75 of the previous paper and confirms that at low intensities the blocking time does not have any influence upon the speed or the shape of the H&D curve.
*e-»*? (50)
Jan., 1939] LATENT IMAGE THEORY 97
(2.512) Approximate Solution at Extremely High Intensities. — At high intensities lim x — > °° . This reduces 42 to :
U-l + JL f
^Tjr
D = Dm (1 - e-*) = Dm(l
Equation 51 is a function of z alone, indicating that no matter how greatly one increases the intensity, a minimum time proportional to the blocking time is required for the formation of a latent image.
The reciprocity failure curve is determined by the fact that t be- comes independent of i. Hence :
£MJ. = 0 (52)
a log i
dlog e _ d log t + d log i _ 1 /^
d log i d log i
Equation 53 defines the reciprocity failure curve as a straight line rising at an angle of 45 degrees.
The shape of the H&D curve for extreme intensity, as expressed by 51, can be interpreted by comparing equation 51 with equation 50 of the previous paper:1 51 is identical with the function resulting from a single step process in a single "layer" of emulsion or in a com- pletely transparent emulsion. That is, the H&D curve at extreme intensities takes the shape of an x-ray characteristic.
(2.51 3) Strict Solution of High-Intensity Equation . — Equation 42 can not be completely solved in analytical form. By partial integration, however, it can be stripped down to residual terms of the form :
This function was discussed and used in the previous paper. * (See equation 59, p. 431, and Fig. 5 of that paper.)
Even with this abbreviating symbol, the solution for R or D re- mains rather complicated :
D = ~ — - '- l+X rx
e
— — e !+* — Z (Fe — Fre) — (1 — z)
*--"-+**, - vi +
(55) From this equation, the curves of Fig. 4 were computed.
98 W. J. ALBERSHEIM [j. s. M. P. E.
(2.514) Formulas for Gamma at High Intensity. — The function for time-scale gamma is nearly as cumbersome as equation 55 because equation 42 does not become integrable by differentiating with regard to*:
yt = (RDoo) = Dm — = 0.434 Dm — -— (56)
d log t d log z dz
•\i*
VT <57>
The intensity-scale gamma, however, can be freed of the integral sign :
— •
(2.52) Computation of Low-Intensity Curves. — As discussed in the computation of high-intensity curves, the constant C of equations 2 and 28 is assumed to approximate the value one. Furthermore, the blocking time is regarded as infinitely short compared to the long exposure times. Thus equation 28 is transformed into :
kv = i + 0.5/ ± V(i + 0.5/)2 - i* = i + 0.5/ ± Vfi + 0.25/2 (55) The following new variables are introduced :
i/f = x (60)
ft = z (61)
2 = k/f (62) This transforms 18 into:
r = 1 +
with q = x + Vs =»= Vx + l/4 (64)
(2.521) Approximate Solution at Relatively High Intensities. — lim
63 can be written in the form :
r = 1 + e~ (3i+22)z/2 I 2? c-(gi-<72)z/2 _
L 2i - 22
^-l-e+(3l-«z2W2j (65)
Jan., 1939] LATENT IMAGE THEORY 99
This approaches the value :
, = 1 + «-[V52- * •- V* - ^t-1 e+VJ,] (66)
and, due to
*Vx < 1,
r = 1 - €-« (e + 1)
^=_ 1 ^ In r
D = RDm =^= ~ [e-*r - €-e - Fe + Fer] (70)
This equation is again identical with equation 79 of the previous paper, confirming that at high intensities the blocking time does not influence speed or shape of the H&D curves.
(2.522) Approximate Solution at Extremely Low Intensities. — Under these conditions,
lim x ->• 0 (71)
2l = 1 + * = 1 (72)
22 = x* (73)
r = 1 - e~*2z =^ 1 — €~' with (74)
j = x*z (75)
I? = -!_ CX r <^ = 1 f r
\nrJXT x ~ 2lnrjj^ j
(76)
The density becomes a function of j alone. The reciprocity failure curve is determined by the equation :
j = constant (78)
d (long x2) + d log z = 0 (73)
2d (log i) = d (log 0 = 0 (80)
d (log e) = d (log *) + d (log 0 = - d log t (&Z)
The reciprocity failure curve becomes a straight line sloping downward at an angle of 45 degrees.
The shape of the H&D characteristic 77 approaches that of a single step process, but with a low transparency, equal to the square of the actual transparency r. Accordingly, one sees in Fig. 5 that the toe of
100 W. J. ALBERSHEIM [j. s. M. P. E.
the extreme right curve becomes rounded, but that the straight-line portion extends way up toward the shoulder.
(2.523) Strict Solution of Low-Intensity Equation. — We have :
R = - j_ r ** ( i + _IL_ «-«. — «L_ €-522 ) (82}
In T Jrx x \ qi - q2 ?i ~ §2 /
__i_,!. ( }
In T J rx x qi — qz
In the first integral of 83 substitute q\ = m* (84) One finds:
x ^ mz — m (85)
dx •= 2m - 1 (£0)
32 = (m - I)2 (87)
In the second integral of 83 substitute q. = »2 (88)
One finds :
x = n* + n (89)
dx = 2n + 1 (90)
<Z2 = (n + I)2 (W) This transforms 83 into :
/0.5 +V0.25 + a: ^lic-«^ m 5+V0.25 + TX
These simplified integrals can not be solved completely. But by partial integration they can be stripped to integrals of the above- mentioned type F(e) and to probability integrals defined as :
which can be found in tables. The solution becomes :
Jan., 1939] LATENT IMAGE THEORY 101
in which equation :
ai = Vz (0.5 4- V0.25 + *) (95}
a2 = Vz(0.5 + V0.25 + r *) (96)
b, = V7(-0.5 + V0.25 + *) (57)
&2 = Vz (-0.5 + \/0.25 + rx) (98)
(2.524) Gamma at Low Intensity. — The time-scale and intensity- scale gammas can be found by differentiation of equation 82 with respect to log / and log i, in a manner analogous to that shown under 2.514. The calculations have been omitted from this appendix be- cause in motion picture sound recording the exposure range is gen- erally not in the low-intensity part of the reciprocity failure curve.
(3) Equations of Reciprocity Failure Curve
The concepts of blocking time and fading time were introduced into the theory in order to account for the reciprocity law failure. It will therefore be shown by the following derivation that, and how, the reciprocity failure curve is determined by the H&D curve 29.
For a given emulsion and development, Dm, r, tb, and Tf are con- stants. k is a function of iv, and the integral 29, a function of iQ and / only. (The suffix of i0 will be omitted below where no misunder- standing is possible.)
Reciprocity curves are plotted with log e, that is, log (it) as ordinate and log i as abscissa. The density is held constant for any given curve. Since log i and log / are the only independent variables the constancy of D is expressed by :
d log e = d log (it) = d log i + d log / (101)
Equation 102 is the required relation between ordinate and abscissa of the reciprocity failure curve.
102 W. J. ALBERSHEIM [j. s. M. p. E.
(4) Reciprocity Curve and Intensity — to Time-Scale Gamma Ratio
In the "straight-line" region of the H&D curves, the partial differ- entials are denned as :
dD/8 log i = 7» (intensity-scale gamma) (103}
D D/D log t == yt (time-scale gamma) (104} Hence 102 may be rewritten in simplified form :
The slope of the reciprocity failure curve equals one minus the ratio of intensity-scale gamma to time-scale gamma. At high intensities, such as used in sound-film recording, this slope is positive; hence the intensity-scale gamma is smaller than the time- scale gamma.
SYMBOLS
Symbol Definition Dimension
c = ** = t*Ti
D = Density
D = Saturation density
e = it = relative exposure
/ = 1/7/ = fading constant sec."1
i*x F(x) = I (\ — e~x} dx/x = integral function
Jo
g = fraction of activated grains in an emulsion layer i = l/r» = relative intensity sec."1
p = probability factor
2 Cx
Px = — — I €—x*dx = probability function
^/TfJO
r = fraction of exposed grains in an emulsion layer
R = fraction of exposed grains in the entire emulsion
t = exposure time sec.
tb = blocking time sec.
/2 = electron time interval for second step sec.
Tf = fading time sec.
Ti = electron time interval for first step sec.
u = absorption constant cm. -1
y = extension into depth of emulsion cm.
Y = total thickness of emulsion cm.
a, b, k, j, m, n, q, U, V, x, z = auxiliary symbols, explained in
appendix
e = basis of natural logarithms
r = transparency of emulsion
6 = partial differential
DISCUSSION
MR. ALBURGER: What is the mechanism by which the electrons deposit the silver atoms on the crystal surface?
MR. ALBERSHEIM: I am not a physicist; I can only guess that every atom in the molecular or crystal array has a certain electrical field surrounding it, and we
Jan., 1939] LATENT IMAGE THEORY 103
know that unless the electron has a certain speed it will be captured. A sharp corner produces a strong electric field; in ordinary wire we have corona effects that we would not have if the wire were round and polished. Something like that happens in the crystal, and at points of physical or chemical irregularity the electric field becomes strong enough to capture and retain the electron. When it is captured the excess electron will be attracted to the silver and rip it loose from the bond to the adjacent chlorine atom, and deposit it no longer as an ion but as a silver atom. The bromide shifts, and if it finds a resting place in the adjacent gelatin matrix it will probably come to rest there. *
MR. GOLDSMITH: If a fully exposed negative is wound up on a reel over a nega- tive of a much less brightly illuminated subject, and the entire negative is pre- served some little time before development, is there found to be any trace of image transfer due to light re-emission from one end of the film to the other?
MR. ALBERSHEIM : I have not found it in the literature, but by word of mouth it has been reported to me that such is the case, that under some conditions a pic- ture can be transferred from one emulsion to an adjacent one. It may be that this effect is not as dangerous as it seems, because the re-emitted electrons have a threshold value and it is possible that it might be easier to obtain the effect if the second emulsion has been sensitized to infrared.
MR. DAVIS: I think the transfer of the picture from one film to another is the work of Sir William Abney, of England, some years ago, who made this experi- ment. He coated a plate and exposed it, and coated another emulsion on top ; then after developing, he stripped the coat and found a picture on the second coating. This probably was a development effect and not a bona fide latent image transfer.
MR. FRAYNE: In view of the fact that the energy of the bullets you speak of is directly proportional to the frequency of the light, is the shape of the catenary curves dependent upon the frequency of the light that is used?
MR. ALBERSHEIM: The influence of color is surprisingly small. I thought there would be such an effect, but this was disproved by the Kodak Research Labora- tories. Webb made an investigation of the influence of color from green, yellow, and reddish light, so far as the emulsion would take to ultraviolet of 3600 A, and the curves, while they came to different densities, were surprisingly close to parallelism. The curve seems just to shift in intensity, but not in character.
MR. FRAYNE: Then in this case how do you explain the change of gamma with wavelength?
MR. ALBERSHEIM: That is probably due to a resonance effect. The emulsion is most sensitive to a certain wavelength, from 4000 to 4400 A. So long as the impinging light falls within that range nearly every grain will be exposed, and high ultimate densities and high gammas result. If we go down to 3500 A, many grains will not be exposed at all, so the emulsion acts as if it had fewer grains. We get lower gamma and lower ultimate density, and a coarser grained picture, relatively speaking. The grains are as big but there are fewer available.
MR. GOLDSMITH: Would you assume that the re-emitted light is of the same wavelength as the original light producing the image? In other words, if a colored object is photographed, would a colored image be released?
* Experiments conducted after the date of this discussion showed trace of this effect.
104 W. J. ALBERSHEIM
MR. ALBERSHEIM: I believe not. No matter how hard the light the electron will probably lose some energy, and when it is finally absorbed it is absorbed with just enough energy to liberate the silver atom. The excess is dissipated, then, perhaps as light or heat, so when the electron is re-emitted it will probably be re- emitted nearly monochromatically.
MR. JONES: At the ultraviolet end, at least, the exposing radiation is absorbed by the thin layers, so you are working with a thinner and thinner emulsion, which of course gives a lower gamma. That is purely absorption. You do not have to invoke resonance to explain that.
MR. ALBERSHEIM: If the emulsion were exposed to ultraviolet of sufficient density you would finally penetrate through, so that the ultimate density at very high exposures would still be the same. It would take very much more light to penetrate to the bottom, and I believe there must be some other effect involved because the ultimate gamma is lower. Also, if you expose with red light or green- ish light, which penetrates all the way through the emulsion, you still get the lower gamma. There may be a superposition of two effects there.
MR. SANDVIK: If the change of gamma with wavelength is a resonance phe- nomenon, how would you explain the change in gamma when you use yellow dye in an emulsion and use blue light?
MR. ALBERSHEIM: That would probably be due to the absorption effect that Dr. Jones has mentioned. However, the resonance effect is present because there is a fairly narrow absorption band in most emulsions. A single silver halide crystal exposed to light has a resonance frequency at about 4000 A where it ab- sorbs the maximum number of photons and is photographically most effective.
MR. SANDVIK: It does that no matter what wavelength radiation is lost. The gamma is greatly decreased to the extent that the absorption takes place with the wavelength that is used.
MR. ALBERSHEIM: I am glad to hear so. In that case we do not need ultra- violet for the sound-films to obtain reduced gamma. We can use the yellow dye, which we have been preferring all along.
THE EVALUATION OF MOTION PICTURE FILMS BY SEMIMICRO TESTING*
J. E. GIBSON** AND C. G. WEBERf
Summary. — Test methods for the evaluation of motion-picture film for permanent records require test specimens too large to be removed from certain archival films. To assist those charged with the preservation of such films in determining the quality and checking the condition of them, suitable semimicro methods were developed for acidity, viscosity, and residual hypo content. Specimens as small as 7 mg. in weight, removed from the film with a small hand punch, gave satisfactory results for the purpose.
(I) Introduction
(II) Experimental testing (1) Acidity
(2} Specific viscosity (3) Residual hypo
(III) Summary and conclusions
(I) INTRODUCTION
Certain repositories, such as The National Archives and some film libraries, are called upon to preserve films which can not be tested by the methods usually recommended for the evaluation of film for permanent records. From these films it is not possible to obtain test specimens of sufficient size for the usual tests without destroying some of the photographic images or making the film unserviceable otherwise. It is important that the condition of such films be de- termined. The nitrate films are chemically unstable, and successful preservation of records contained on them requires that they be ex- amined periodically so that disintegration can be anticipated and duplicates made of the records before they are impaired by visible deterioration. Good acetate film is stable, but it should be tested before placing it in storage to find if it was properly made and proc- essed. Also, subsequent testing of it may be desirable, particularly
* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 3, 1938.
** The National Archives, Washington, D. C. t National Bureau of Standards, Washington, D. C.
105
106 J. E. GIBSON AND C. G. WEBER [j. s. M. P. E.
if it should be exposed to unfavorable storage conditions. The semimicro methods described in this article were developed to permit the testing of such films without removing test specimens large enough to impair the film as regards legibility and serviceability.
(II) EXPERIMENTAL TESTING
In studies1 of the stability of photographic films, tests for copper number, viscosity, acidity, residual hypo (sodium thiosulfate), and flexibility were found to be of value. These tests were recommended2 for the evaluation of film for permanent records. Hence, the micro methods developed were modifications of some of these methods. The value of each of the proposed methods was determined by testing films that had been subjected to accelerated aging at 100°C in oven- dry air for various periods of time. The data are thus comparable with those obtained by Hill and Weber1 with test specimens of normal amount. The micro tests were made with test specimens weighing only 7 mg. each, which were removed from the films with a J /4-inch hand punch without causing appreciable damage to the film. The value of the micro test was judged by comparing the results of them with results obtained with the usual methods. The micro methods developed were for acidity, viscosity, and residual hypo.
(1) Acidity. — The acidity of the film was determined in the follow- ing manner. A single punching (wt. 0.007 g.) of film, including both base and emulsion, was transferred to a test tube and 5 ml. of acetone, containing 10 per cent of water by volume, was added. After com- plete dispersion of the film base, the acidity in £H units was deter- mined by means of a commercial micro £H-meter. The results are shown in Fig. 1 in comparison with ^>H values obtained with the same apparatus for seven punchings of film weighing 0.049 gram in 5 ml. of acetone containing 10 per cent of water by volume.
The water and acetone were purified by distillation and the com- bined solvent had a pH of 7 ^ 0.4. Duplicate determinations on the film agreed within 0.1 pH unit.
(2) Specific Viscosity. — A punching of film (wt. 0.007 g.) was transferred to a test tube and dissolved in 5 ml. of acetone measured at 30° =*= 0.02°C. After solution of the film base was complete and the mixture homogeneous, 3 ml. of the solution was transferred to an Ostwald viscosity pipette immersed in a constant-temperature bath (30° ± 0.02°C), and allowed to stand until temperature equilibrium was reached. The time of flow of the solution through the capillary
Jan., 1939] EVALUATING FILMS BY SEMIMICRO TESTING
107
of the pipette was measured with a stop-watch which could be read to one-fifth second. The time of flow of the pure solvent was also measured. Not less than three or four determinations were made for each solution, the values agreeing within two- or three-tenths of a second. The relative viscosity was then calculated as the ratio of the time of flow of the solution to the time of flow of the solvent.
Fig. 2 shows the results of these measurements compared with re- sults obtained by Hill and Weber with one-gram samples. The different scales were necessary because different values are obtained by the two methods.
USUAL METHOD -7 PUNCHINGS (.049 6M >
Q ACETATE FILM
• NITRATE FILM
SEMI-MICRO METHOD -I PUNCHING (.007 GM)'
§ ACETATE FILM NITRATE FILM
10 20
TIME OF HEATING- DAYS
FIG. 1. Effects of accelerated aging on pH of cellulose acetate and cellulose nitrate films ; results obtained by the semimicro method compared with those obtained on larger test specimens.
(3) Residual Hypo. — The method used for detecting the presence of residual hypo (sodium thiosulfate) in films is a modification of the test proposed by Crab tree and Ross.3 The method as modified con- sists in placing a single punching of film on a glass slide, adding two drops of mercuric chloride test solution to the specimen in such a manner that the solution flows over the specimen and onto the glass, and observing any turbidity that develops in the solution. The test solution contains 25 grams of mercuric chloride and 25 grams of potassium bromide in a liter of aqueous solution. The film is placed on the glass with the emulsion side up, and is allowed to stand for 2 or 3 minutes after the addition of the test solution. It was found-
108
J. E. GIBSON AND C. G. WEBER [j. s. M. P. E.
that any turbidity of the solution can be best detected with the un- aided eye when the glass is held in the light so that the angle of in- cidence is approximately 90 degrees.
If sodium thiosulfate is present, it reduces mercuric ion, and an in- soluble mercurous compound is formed which causes turbidity. If no thiosulfate is present, the solution on the glass remains clear, al- though the silver image is bleached white. Positive tests were ob- tained in this manner on single punchings taken from film that con- tained less than 0.05 mg. of hypo per square-inch. Positive tests
•WAI METHOD ACETATE FILM NITRATE FILM MI-MICRO METHOD
§ ACETATE FILM NITRATE FILM
TIME OF HEATING -DAYS
FIG. 2. Effects of oven aging on viscosity of cellulose acetate and cellulose nitrate films as determined by the semimicro methods and by the usual methods.
were also obtained with solutions containing 10 parts of hypo per million parts of water when a large drop of the solution was added to a drop of the test solution.
(ni) SUMMARY AND CONCLUSIONS
Motion picture films that can not be sampled for testing by the usual methods can be tested by the semimicro methods. The ap- proximate quality and condition of the film can be determined by tests for acidity, viscosity, and residual hypo, using specimens weigh- ing only 7 mg. each, which can be taken from the film by means of a small hand punch without appreciable damage to the film. These methods are not recommended for use in selecting permanent record film. However, they are recommended to archivists and librarians for determining the condition of finished films given them for custody.
Jan., 1939 ] EVALUATING FlLMS BY SEMIMICRO TESTING 109
With these tests, the approximate condition of the films can be found, and the necessity of making duplicate copies can be determined be- fore the damage to the films by deterioration is serious enough to be visible. The values obtained by the semimicro methods will differ somewhat from those obtained by the usual methods, but they ap- pear to show the extent of deterioration under accelerated aging equally well. When absolute values are used in judging the condi- tion of a film in question, those obtained by the semimicro methods should be compared with values obtained for new film by these methods.
REFERENCES
1 /. Research, Nat. Bur. Standards, 17 (1936), p. 871; RP950.
* Muse. Pub. Nat. Bur. Standards, M158 (1937).
3 CRABTREE, J. I., AND Ross, J. F.: "A Method of Testing for the Presence of Sodium Thiosulfate in Motion Picture Films," J. Soc. Mot. Pict. Eng., XIV (April, 1930), No. 4, p. 419.
DISCUSSION
MR. CRABTREE: Our recent researches have indicated that the milky compound formed by reaction of the mercuric chloride with hypo is not mercurous chloride but, rather, a double compound of mercuric sulfide and mercuric chloride having the formula 2HgS HgCl2. Such a compound has been described by H. Rose (Poggendorff, Annalen der Physik, 13: 59, 1828) and by Th. Poleck and C. Goercki (Berichte, 21: 2412-2417, 1888).
CURRENT LITERATURE OF INTEREST TO THE MOTION PICTURE
ENGINEER
The editors present for convenient reference a list of articles dealing with subjects cognate to motion picture engineering published in a number of selected journals. Photostatic copies may be obtained from the Library of Congress, Washington, D. C., or from the New York Public Library, New York, N. Y. Micro copies of articles in magazines that are available may be obtained from the Bibliofilm Service, Depart- ment of Agriculture, Washington, D. C.
Journal of the Acoustical Society of America
10 (Oct., 1938), No. 2
Absorption of Sound in Carbon Dioxide and Other Gases (pp. 89-97)
Measurement of Absorption in Rooms with Sound Ab- sorbing Ceilings (pp. 98-101)
Absorption Effects in Sound Transmission Measure- ments (pp. 102-104)
Absolute Sound Measurements in Liquids (pp. 105-111) Theory of the Chromatic Stroboscope (pp. 112-118)
Adjustable Tuning Fork Frequency Standard (pp. 119-
127) Recent Advances in the Use of Acoustic Instruments for
Routine Production Testing (pp. 128-134) Frequency Ratios of the Tempered Scale (pp. 135-136) Harmonic Structure of Vowels in Singing in Relation to
Pitch and Intensity (pp. 137-146) Apparatus for Direct-Recording the Pitch and Intensity
of Sound (pp. 147-149)
American Cinematographer
19 (Oct., 1938), No. 10
Flashes Across Nearly Sixty Years (pp. 403-404) Dunning Has Three-Color Process Now Ready to Go
(pp. 406, 416) Mole-Richardson Introduces Duarc, New Automatic
Broadside (pp. 407, 416) Ingenious Accessories Simplify Making of Special Effects
Shots (pp. 408, 410)
100 Watter Throws 150 — and Whiter (p. 411) American Cameramen Lead. . . Pasternak (pp. 412-414)
110
V. O. KNUDSEN AND E. F. FRICKE
J. R. POWER
P. E. SABINE AND L. G. RAMER E. KLEIN R. W. YOUNG AND
A. LOOMIS
O. H. SCHUCK
B. FOULDS
C. WILLIAMSON
B. STOUT
J. OB AT A AND R. KOBAYASHI
J. GEVAERT
G. TEAGUE J. PASTERNAK
CURRENT LITERATURE
111
American Cinematographer
19 (Nov., 1938), No. 11
What's Wrong with Cinematography? (pp. 449, 457) Reeves Single System Sound Fits Any Camera (pp. 454-
455)
New Berndt-Maurer Sound Tract (pp. 456) 20th-Fox Installs New Make-Up Lamps (p. 479)
British Journal of Photography
85 (Sept. 9, 1938), No. 4088 Aluminum as a Photographic Base (pp. 568-570)
Journal of the British Kinematograph Society
1 (Oct., 1938), No. 3
Modern Electric Discharge Lamps and Their Applica- tion to Kinematography (pp. 158-174) Volume Range Expanders (pp. 175-187) Manufacture of Motion Picture Film (pp. 188-204) An Optical System for Sound Reproduction (pp. 209- 213)
Bulletin de la Societe Francaise de Photographic et de Cinematographic
25 Sere. 3 (Sept., 1938), No. 9
Sur L'Obtention de Negatifs Photographiques a Grains Fins a Partir d'Emulsions ou d'Images a Gros Grains. (Obtaining Fine Grain Negatives Starting with Large Grain Emulsions or Images) (pp. 145-150)
Educational Screen
17 (Sept., 1938), No. 7
Motion Pictures — Not for Theaters, Pt. I (pp. 211- 215)
17 (Oct., 1938), No. 8 Motion Pictures — Not for Theaters. Pt. II (pp. 249-
253) Preparing Sound Film Strips (pp. 254-256)
Electronics
11 (Oct., 1938), No. 10
A Laboratory Television Receiver — IV (pp. 16-19) A Shielded Loop for Noise Reduction in Broadcast Re- ception (pp. 20-22) Squeeze or Matted Track (p. 23) An Electric Timing Device (pp. 28-29)
Ideal Kinema
6 (Oct. 13, 1938), No. 71
The Stableford All-Metal Screen, How It Is Constructed (P- 33)
H. W. GREENWOOD
W. R. STEVENS J. Mom A. E. AMOR
J. H. McLsoD AND F. E. ALTMAN
A. SEYEWETZ
A. E. KROWS
A. E. KROWS C. R. THOMAS
D. G. FINK
S. GOLDMAN J. K. HILLIARD R. W. CARLSON
112
CURRENT LITERATURE
Kinematographic Weekly
259 (Sept. 29, 1938), No. 1641 Metals as Base for Picture Film (p. 36)
260 (Oct. 27, 1938), No. 1645 Metal Film Projection (p. 41)
Television Principles in Kinematography (p. 41)
International Photographer
10 (Oct., 1938), No. 9 Duplex Production Printer (pp. 6-7) Ultra-Fidelity Recorder (p. 7) Gevaert Revives 35-Mm. Raw Stock (p. 9) Technicolor Expands (p. 9) Projection-Revision of SMPE Standards (pp. 24-27)
Kinotechnik
20 (Oct., 1938), No. 10 Sicherheitsnlm im Normalformat (35 Mm. Safety Film)
(pp. 255-256) Bildfilm und Magnetton (Magnetic Sound Recording on
Film) (pp. 256-257)
Methoden zur Messung des photographischen Gleich- richtereffektes (Method of Measuring the Photo- graphic Rectifying Effect) (pp. 258-264)
Zwei neue Aufnahme-Materialen ; Agfa Superpanfilm und Agfa Ultrarapidfilm (Two New Films; Agfa Superpan and Agfa High-Speed Film) (pp. 264-267)
Moderne Wiedergabegerate fur 16-Mm.-Tonfilm (Mod- era 16-Mm. Sound-Film Projectors) (pp. 268-269)
International Projectionist
13 (Oct., 1938), No. 10 Advance Preparations Minimize Sound Emergencies
(pp. 7-10)
Television and Its Effect Upon the Motion Picture Theatre) (pp. 12-14)
A Higher-Efficiency Condensing System for Tungsten- Filament Projectors (pp. 14-16)
Projection Possibilities of Mercury Vapor Discharge Lamp (pp. 17-18)
Photographische Korrespondenz
74 (Oct., 1938), No. 10
Fortschritte der Kinematographie im Jahre 1937 (Prog- ress of Photography in 1937) (pp. 164-167)
C. N. BATSEL
J. GRASSMAN
H. PETERSEN
A. NARATH AND W. Vox
A. SCHILLING
WEINBERGER
A. NADELL
F. WALDROP AND J. BORKIN
F. E. CARLSON R. H. CRICKS
H. PANDER
SPRING, 1939, CONVENTION SOCIETY OF MOTION PICTURE ENGINEERS
HOLLYWOOD ROOSEVELT HOTEL HOLLYWOOD, CALIFORNIA APRIL 17th-21st, INCLUSIVE
Officers and Committees in Charge
E. A. WILLIFORD, President
N. LEVINSON, Executive V ice-President
W. C. KUNZMANN, Convention Vice-President
J. I. CRABTREE, Editorial Vice-President
L. RYDER, Chairman, Pacific Coast Section
H. G. TASKER, Chairman, Local Arrangements Committee
J. HABER, Chairman, Publicity Committee
Pacific Coast Papers Committee
L. A. AICHOLTZ, Chairman
O. O. CECCARINI W. A. MUELLER
G. CHAMBERS H. G. TASKER
L. D. GRIGNON W. H. ROBINSON, JR.
Reception and Local Arrangements
H. G. TASKER, Chairman
N. LEVINSON G. F. RACKETT E. HUSE
K. F. MORGAN H. W. MOYSE L. L. RYDER
P. MOLE W. MILLER J. O. AALBERG
A. M. GUNDELFINGER J. A. BALL R. H. McCULLOUGH
H. W. REMERSCHIED W. A. MUELLER J. M. NICKOLAUS
G. S. MITCHELL C. L. LOOTENS E. H. HANSEN
Registration and Information
W. C. KUNZMANN, Chairman
S. HARRIS C. W. HANDLEY
E. R. GEIB W. R. GREENE
Hotel and Transportation
G. A. CHAMBERS, Chairman
W. C. HARCUS C. DUNNING W. E. THEISEN
G. HOUGH E. C. RICHARDSON D. P. LOYE
B. KREUZER K. STRUSS O. O. CECCARINI H. W. REMERSCHIED J. C. BROWN C. J. SPAIN
113
114 SPRING, 1939, CONVENTION [j. s. M. p. E.
Convention Projection
H. GRIFFIN, Chairman
J. O. AALBERG H. A. STARKE J. DURST
C. W. HANDLEY L. E. CLARK R. H. McCuLLOUGH
W. F. RUDOLPH M. S. LESHING H. C. SILENT
J. M. NICKOLAUS A. F. EDOUART H. I. REISKIND
J. K. HILLIARD I. SERRURIER W. W. LINDSAY, JR.
Officers and Members of Los Angeles Projectionists Local No. 150
Banquet and Dance
N. LEVINSON, Chairman
H. T. KALMUS G. S. MITCHELL G. F. RACKETT
E. HUSE P. MOLE J. O. AALBERG
L. L. RYDER H. G. TASKER K. F. MORGAN
C. DUNNING W. MILLER H. W. MOYSE
G. A. MITCHELL R. H. MCCULLOUGH J. L. COURCIER
Ladies' Reception Committee
MRS. N. LEVINSON, Hostess
assisted by
MRS. E. C. RICHARDSON MRS. P. MOLE MRS. E. HUSE
MRS. G. F. RACKETT MRS. C. W. HANDLEY MRS. L. L. RYDER
MRS. H. W. MOYSE MRS. K. F. MORGAN MRS. J. O. AALBERG
MRS. H. G. TASKER MRS. W. MILLER MRS. R. H. MCCULLOUGH
MRS. L. E. CLARK MRS. A. M. GUNDELFINGER MRS. C. DUNNING
Publicity
J. HABER, Chairman
L. A. AICHOLTZ W. R. GREENE S. HARRIS
W. A. MUELLER G. CHAMBERS A. M. GUNDELFINGER
Equipment Exhibit
J. G. FRAYNE, Chairman
P. MOLE C. R. DAILY H. W. REMERSCHIED
J. DURST S. HARRIS C. N. BATSEL
Headquarters
Headquarters of the Convention will be the Hollywood-Roosevelt Hotel, where excellent accommodations are assured. A reception suite will be provided for the Ladies' Committee, and an excellent program of entertainment will be arranged for the ladies who attend the Convention.
Special hotel rates, guaranteed to SMPE delegates, European plan, will be as follows :
One person, room and bath $ 3 . 50
Two persons, double bed and bath 5 . 00
Two persons, twin beds and bath 6 . 00
Parlor suite and bath, 1 person 8 . 00
Parlor suite and bath, 2 persons 12 . 00
Jan., 1939] SPRING, 1939, CONVENTION 115
Indoor and outdoor garage facilities adjacent to the Hotel will be available to those who motor to the Convention.
Members and guests of the Society will be expected to register immediately upon arriving at the Hotel. Convention badges and identification cards will be supplied which will be required for admittance to the various sessions, the studios, and several Hollywood motion picture theaters.
Railroad Fares
The following table lists the railroad fares and Pullman charges:
Railroad
Fare Pullman
City (round trip) (one way)
Washington $132.20 $22.35
Chicago 90.30 16.55
Boston 147.50 23.65
Detroit 106.75 19.20
New York 139.75 22.85
Rochester 124.05 20.50
Cleveland 110.00 19.20
Philadelphia 135.50 22.35
Pittsburgh 117.40 19.70
The railroad fares given above are for round trips, sixty-day limits. Arrange- ments may be made with the railroads to take different routes going and coming, if so desired, but once the choice is made it must be adhered to, as changes in the itinerary may be effected only with considerable difficulty and formality. Dele- gates should consult their local passenger agents as to schedules, rates, and stop- over privileges.
Technical Sessions
The Hollywood meeting always offers our membership an opportunity to be- come better acquainted with the studio technicians and production problems, and arrangements will be made to visit several of the studios. The Local Papers Committee under the chairmanship of Mr. L. A. Aicholtz is collaborating closely with the General Papers Committee in arranging the details of the program. Complete details of the program will be published in a later issue of the JOURNAL.
Semi- Annual Banquet and Dance
The Semi- Annual Banquet of the Society will be held at the Hotel on Thursday, April 20th. Addresses will be delivered by prominent members of the industry, followed by dancing and entertainment. Tables reserved for 8, 10, or 12 persons; tickets obtainable at the registration desk.
Equipment Exhibit
An exhibit of newly developed motion picture equipment will be held in the Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish to enter their equipment in this exhibit should communicate as early as possible with the general office of the Society at the Hotel Pennsylvania, New York, N. Y.
116 SPRING, 1939, CONVENTION
Motion Pictures
At the time of registering, passes will be issued to the delegates to the Conven- tion, admitting them to the following motion picture theaters in Hollywood, by courtesy of the companies named: Grauman's Chinese and Egyptian Theaters (Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These passes will be valid for the duration of the Convention.
Inspection Tours and Diversions
Arrangements are under way to visit one or more of the prominent Hollywood studios, and passes will be available to registered members to several Hollywood motion picture theaters. Arrangements may be made for golfing and for special trips to points of interest in and about Hollywood.
Ladies' Program
An especially attractive program for the ladies attending the Convention is being arranged by Mrs. N. Levinson, hostess, and the Ladies' Committee. A suite will be provided in the Hotel, where the ladies will register and meet for the various events upon their program. Further details will be published in a succeeding issue of the JOURNAL.
Points of Interest
En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks.
Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Li- brary and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at Ocean Park and Venice, Calif.; famous old Spanish missions; Los Angeles Mu- seum (housing the SMPE motion picture exhibit); Mexican village and street, Los Angeles.
In addition, numerous interesting side trips may be made to various points throughout the west, both by railroad and bus. Among the bus trips available are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, and Palm Springs, and special tours may be made throughout the Hollywood area, visiting the motion picture and radio studios.
On February 18, 1939, the Golden Gate International Exposition will open at San Francisco, an overnight trip from Hollywood. The Exposition will last throughout the summer so that opportunity will be afforded the eastern members to take in this attraction on their convention trip.
SOCIETY ANNOUNCEMENTS
ELECTION OF SECTION OFFICERS
Results of the election of officers and managers of the Mid- West and Pacific Coast Sections of the Society are as follows:
(Mid-West}
*S. A. LUKES, Chairman
C. H. STONE, Past-Chairman *J. A. DUBRAY, Manager
*G. W. BAKER, Sec.-Treas. **O. B. DEPUE, Manager
(Pacific Coast) *L. RYDEE, Chairman
J. O. AALBERG, Past-Chairman *C. W. HANDLEY, Manager
*A. M. GUNDELFINGER, Sec.-Treas. **W. MILLER, Manager
* Term expires December 31, 1939. ** Term expires December 31, 1940.
Elections of officers and managers of the Atlantic Coast Section are now in progress and will be announced in the next issue of the JOURNAL.
ATLANTIC COAST SECTION
At a meeting of the Section held on December 13th at the studios of RCA Photophone, Inc., New York, a paper was presented by F. C. Gilbert and E. S. Seeley of the Altec Service Corporation, New York, on the subject of "The Adjustable Equalizer as a Tool for Selecting the Best Response Characteristics." This equalizer is a device that can be inserted into theater reproducing systems for determining with a given horn system what characteristic is best in a given house. It is portable and can be carried into the auditorium, and has an ex- tremely wide range of variation.
The paper was presented by Mr. Seeley and aroused considerable interest among the members attending the meeting, as evidenced by the protracted discussion held at the close of the presentation. A demonstration of the equalizer accompanied the presentation.
MID-WEST SECTION
At a meeting held at The Western Society of Engineers, Chicago, on December 6th, Mr. J. Frankenberg presented a paper dealing with "Mechanical Sound Recording of Film." The meeting was well attended and the presentation was discussed at considerable length.
Announcement of the officers and managers of the Section for the year 1939 was made as listed above.
117
118 SOCIETY ANNOUNCEMENTS
PACIFIC COAST SECTION
On December 15th a meeting of the Section was held at the Walt Disney Studios in Hollywood, at which time a demonstration of the recording spectro- photometer and the Disney multiplane camera was given by the technical staff of the Walt Disney Studios. On account of limited accommodations, the meeting was open to only members of the Society and was well attended. The presenta- tion elicited much interest and discussion.
CONVENTION ACKNOWLEDGMENTS
Acknowledgment is due to many companies and persons for their cooperation in arranging and conducting the Detroit Convention, held on October 31st- November 2nd, with headquarters at the Hotel Statler. General facilities of the Convention were arranged by Mr. W. C. Kunzmann, Convention Vice-P resi- dent; Messrs. H. Griffin, J. Frank, Jr., and G. Friedl, Jr., in charge of projection facilities; Mr. K. Brenkert, Chairman of the Local Arrangements Committee; A. J. Bradford and J. F. Strickler on the Local Arrangements Committee; Mrs. J. F. Strickler, hostess in charge of the Ladies' Committee; Mr. J. Haber and F. Johntz of the Publicity Committee; and Mr. E. R. Geib, Chairman of the Member- ship Committee.
Credit for the papers program and technical arrangements are due to Mr. J. I. Crabtree, Editorial Vice-P resident, and Mr. G. E. Matthews, Chairman of the Papers Committee.
Among the companies contributing equipment and service to the Convention were the following: International Projector Corporation, National Carbon Company, National Theatre Supply Company, Raven Screen Company, East- man Kodak Company, Bausch & Lomb Optical Company, RCA Manufacturing Company, Brenkert Light Projection Corporation, Jam Handy Pictures Cor- poration, and the Detroit Local 199 IATSE.
The Society is indebted to the following companies for the films loaned for the motion picture performance held on the evening of Monday, October 31st: RKO Radio Pictures, Paramount Pictures, Inc., Eastman Kodak Company, Technicolor Motion Picture Corporation, March of Time, and Walt Disney Productions, Ltd.
Acknowledgment is due also to the United Detroit Theaters Corporation and the Fox Detroit Theater for supplying passes to members and guests during the week of the Convention.
ADMISSIONS COMMITTEE
The following applicants have been admitted by vote of the Board of Governors to the Active grade:
CASE, P. H. HONAN, E. M.
28 West 23rd St., 6601 Romaine St.,
New York, N. Y. Los Angeles, Calif.
FESSLER, F. D. SAWYER, C. R.
4431 West Lake St., 6601 Romaine St.,
Chicago, 111. Los Angeles, Calif.
WALKER, H. S.
1620 Notre Dame St. West, Montreal, Canada
JOURNAL
OF THE SOCIETY OF
MOTION PICTUTE ENGINEERS
Volume XXXII February, 1939
CONTENTS
Page Some Television Problems from the Motion Picture Standpoint
G. L. BEERS, E. W. ENGSTROM, AND I. G. MALOFF 121
Some Production Aspects of Binaural Recording for Sound
Motion Pictures
W. H. OFFENHAUSER, JR., AND J. J. ISRAEL 139
Coordinating Acoustics and Architecture in the Design of the Motion Picture Theater. . C. C. POT WIN AND B. SCHL ANGER 156
Characteristics of Film Reproducer Systems
F. DURST AND E. J. SHORTT 169
Some Practical Accessories for Motion Picture Recording
R. O. STROCK 188
The Lighting of Motion Picture Theater Auditoriums
F. M. FALGE AND W. D. RIDDLE 201
Revised Standard Electrical Charactersitics for Two- Way Re- producing Systems in Theaters, Research Council, Academy of Motion Picture Arts & Sciences 213
Organization of the Work of the Papers Committee
G. E. Matthews 217
Current Motion Picture Literature 225
1939 Spring Convention, Hollywood, Calif 226
Society Announcements 230
JOURNAL
OF THE SOCIETY OF
MOTION PICTURE ENGINEERS
SYLVAN HARRIS, EDITOR
Board of Editors J. I. CRABTREE, Chairman
A. N. GOLDSMITH A. C. HARDY H. G. KNOX
J. G. FRAYNE L. A. JONES G. E. MATTHEWS
E. W. KELLOGG
Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, included in their annual membership dues; single copies, $1.00. A discount on subscription or single copies of 15 per cent is allowed to accredited agencies. Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. Published monthly at Easton, Pa., by the Society of Motion Picture Engineers.
Publication Office, 20th & Northampton Sts., Easton, Pa. General and Editorial Office, Hotel Pennsylvania, New York, N. Y.
West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. Entered as second class matter January 15, 1930, at the Post Office at Easton, Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of Motion Picture Engineers, Inc.
Papers appearing in this Journal may be reprinted, abstracted, or abridged provided credit is given to the Journal of the Society of Motion Picture Engineers and to the author, or authors, of the papers in question. Exact reference as to the volume, number, and page of the Journal must be given. The Society is not responsible for statements made by authors.
OFFICERS OF THE SOCIETY
** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. ** Past-President: S. K. WOLF, RKO Building, New York, N. Y. ** Executive Vice-P resident: N. Levinson, Burbank, Calif.
* Engineering Vice-P resident: L. A. JONES, Kodak Park, Rochester, N. Y. ** Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y.
* Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. ** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio.
* Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y.
* Treasurer: L. W. DAVEE, 153 Westervelt Ave., Tenafly, N. Y.
GOVERNORS ** M. C. BATSEL, Front and Market Sts., Camden, N. J.
* R. E. FARNHAM, Nela Park, Cleveland, Ohio.
* H. GRIFFIN, 90 Gold St., New York, N. Y.
* D. E. HYNDMAN, 350 Madison Ave., New York, N. Y.
* L. L. RYDER, 5451 Marathon St., Hollywood, Calif.
* A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass.
* S. A. LUKES, 6427 Sheridan Rd., Chicago, 111.
** H. G. TASKER, 14065 Valley Vista Blvd., Van Nuys, Calif.
* Term expires December 31, 1939. ** Term expires December 31, 1940.
SOME TELEVISION PROBLEMS FROM THE MOTION PICTURE STANDPOINT*
G. L. BEERS, E. W. ENGSTROM, AND 1. G. MALOFF**
Summary. — -Certain of the characteristics of television have their counterparts in motion pictures, and motion picture film and motion picture practice are applicable to television. Some of the problems and limitations pertaining thereto are outlined, and the following television-image characteristics are briefly discussed: (1) Number of scanning lines and the relationship to image size and viewing distance; (2) number of frames; (3) interlacing.
The effect of film and optical