The motion picture projectionist (Nov 1929-Oct 1930)

26 The Motion Picture Projectionist January, 1930 e Laboratory 16 mm. Sound Recording AT present there are three designs for equipment to be used for showing sound pictures in the home. Several features of this equipment are of more than passing interest to the professional motion picture worker. The three designs are: (1) mechanical synchronization between a phonograph record and the film, (2) the use of a "home" projector using a 35 mm. film, and (3) the use of a 16 mm. projector. By "home talkie" is meant a machine not particularly adaptable for professional use in theatre projection work but which is used for home entertainment, schools, and advertising purposes. There are three means of synchronizing the film with the record, and these are (1) mechanically, as by means of a train of gears coupling the phonograph to the projector, (2) the use of sprocket holes in the film to drive the disc, and (3) by the use of synchronous motors, as in professional work. Space and Speed Problems The recording of sound on 35 mm. film for home talkies presents no problems that have not already been solved in the commercial forms of sound recording. However, the 16 mm. film presents an entirely new set of physical problems, principally the questions of economy of space and the difference in relative speed between 16 mm. and 35 mm. film. It is well to remember that 35 mm. film runs at about three times the relative speed of 16 mm. film. Another important consideration is the fact that the silver grain of the 16 mm. film has an approximate diameter of 1/400 of an inch. Reducing the above facts to simple arithmetic, we find that 16 mm. film travels at the rate of approximately 6 inches per second, and because of the comparatively large grain of the silver particles, the highest frequency possible to record on the present commercial type of 16 mm. film is 2,400 cycles per second. This permits understandable speech reproduction but musical reproduction is subject to severe distortion. Another difficulty in 16 mm. sound recording is that of the slit. For this purpose it has been found necessary to reduce the diameter of the slit used to one-third the professional standard size. Those who are familiar with this phase of the art will, I believe, •Conducted by SAMUEL WEIN agree that the accomplishment of t1 is feat is nothing short of a miracle. New Eastman Grain Other engineering difficulties in connection with this field are certain to be solved within a reasonable period of time. The problem of frequency has been attacked from various angles, and a sufficient number of pictures per second have been recorded on the film to increase the reproduction speed to very nearly 90 feet per minute. This method is not very efficient, however, and it would seem that the' best possible solution lies in using a much smaller grain or using a different type of photographic medium altogether. We are advised that Eastman Kodak Co. has succeeded in producing a much finer grained silver emulsion which will undoubtedly contribute largely to the solution of the problem of grain. The sound slit problem may be nicely solved by using an optical projector in which the film would run continuously instead of intermittently. The problem of space may be solved by having sprocket holes on only one side of the film, or between the pictures, as is now done in the Patnex system. Optical Slits We have recently had occasion to examine the claims of C. Francis Jenkins, of television fame, on the use of "optical slits." The patent referred to is 1,390,445 of September 13, 1921. The optical slit described therein by Jenkins is seen in the accompanying illustration. It will be seen that an incandescent lamp A is in the focal point of a reflector E. This source of light is now focussed through the medium of a lens J and through a diaphragm or course slot C. The source of light is now further reduced to a fine slit by means of a lens D. This light is now focussed through the sound track on the film and onto the photo electric or other form of light sensitive cell. Jenkins Patent Range In discussing this optical slit patent with a number of persons in authority we found them in entire agreement with us in that this Jenkins invention is identical in every respect with the optical slits now so commonly used in the sound head of sound picture apparatus. We are advised by officials of the Jenkins Television Corp. that they have no intentions at the present time of entering the sound picture field, although it is apparent that they have enough "patent background" to warrant their doing so. The many patents held by Jenkins cover almost every phase of the motion picture industry, including the photographic, projection, sound picture and television ends. Complete A. C. Apparatus Developed by Miehling AN interesting experiment in straight A.C. sound picture apparatus operation is now in progress in the laboratory of Rudolph Miehling, sound editor of The Motion Picture Projectionist. Miehling has long subscribed to the view that A.C. operation of sound picture apparatus was not only feasible but desirable, from both the economic and operating efficiency viewpoints. The desire to rid the projection room of storage batteries, a point on which much information has appeared in these columns, led Miehling to compile all available data on the matter and proceed to work out the problem in his laboratory. Certain patent considerations forbid complete disclosure of the Miehling apparatus, particularly with regard to circuit arrangement. Full information on all these points will be published in these columns as soon as practicable. Meanwhile the following C. Francis Jenkins Optical Slit Patent