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Aug., 1940] NEW MOTION PICTURE APPARATUS 207
PROFESSIONAL 16-MM RECORDING EQUIPMENT*
D. CANADY**
Direct variable-density recording is rapidly gaining favor in the 16-mm field. This is to be expected as good 16-mm variable-density recorded track with noise reduction compares favorable with 35-mm track made by commercial motion picture producers. Hollywood technicians are overwhelmingly in favor of the variable-density method and there is little doubt that 16-mm film producers will soon adopt directly variable-density recording as standard practice.
Professional Type 16-mm Sound-onFilm Recorder. — The professional type 16-mm film recorder described here has been designed and built to meet the requirements of the commercial producer of 16-mm films. The complete machine is shown in Fig. 1. Constant film-speed is assured by a rotary stabilizer of the dry type, which is not affected by climatic conditions. All shafts rotate on ball bearings. The recording-drum shaft and recording-drum pad-roller revolve on precision ball-bearings selected for their smooth running qualities. Provision has been made for lateral adjustment of guide flanges and pad-roller pressure is adjustable over a wide range.
A gaseous discharge lamp is used as a light-modulator, and the output is focused on the film by an optical unit of high resolving power. Microscopic examination of frequency runs 30 to 10,000 cps recorded on standard recording emulsion show clean-cut striations up to 9000 cps. As no commercial 16-mm sound projector is capable of reproducing frequencies of this order, the recorder should meet all requirements of 16-mm producers for some time to come.
Faithful recording of high audio frequencies is necessary for good sound quality. Careful and precise adjustment of the optical systems in 16-mm recorders is of the utmost importance. Because of the restricted area available on 16-mm film, there is a definite limit to the number of striations that can be photographed per second.
Under present standards, optimal results can be achieved by using a very narrow slit sharply focused on the film. While optical units can be sharply focused and sealed at the factory, this practice does not permit adjustments being made for tolerances encountered in film stock. Furthermore, a slit image sharply focused on film tightly wrapped around a stationary drum will not necessarily remain in optimal focus when the film is in motion. In film recorders using film-driven, freerunning recording drums mounted on ball-bearings, the distance between the optical unit and the emulsion surface is subject to slight variation due to (1~) types and makes of fUm stock and (2) degree of film flexibility. Film stock varies in thickness according to type and manufacturer. The flex of a film loop changes with respect to age and moisture content of the emulsion. Fresh stock is usually pliable and adheres closely to the surface of the recording drum while old or driedout film is less resilient and has a tendency to "bulge" away from the drum. (Fig. 2.)
*Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received April 15, 1940.
** Canady Sound Appliance Co., Cleveland, Ohio.