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DirectPositive Variable-Area Recording with the Light Valve*
BY LEWIS B. BROWDER
WESTERN ELECTRIC COMPANY, HOLLYWOOD, CALIFORNIA
Summary — By reflecting light from the back surface of the light-valve ribbons and focusing the ribbon edges at the film plane a bilateral or unilateral type of direct-positive variable-area track is obtained. By relocating the recording lamp so that light is transmitted through the space between the ribbons a normal variable-area negative may be obtained.
ANEW FILM RECORDING MACHINE designated as Type RA-1231 was described in the JOURNAL1 in 1946 employing the tight-loop, controlled -compliance type of film drive. As shown, the recorder was equipped with a small, variable-density type of modulator. Since then, there have been described a 200-mil push-pull density modulator2 and a lightvalve-type, double-width, push-pull variable-area modulator3 both of which operate with the same basic film-pulling unit as was shown with the small modulator. In this paper is described the fourth in the series of modulators for use in the Type RA1231 recorder; i.e., a simple, compact, standard variable-area modulator. As in the other modulators, the ribbon light valve is employed as the basic modulating element, the field of application of this device being extended in this modulator to the recording of direct-positive variable-area sound track as well as the standard negative variablearea track.
The direct-positive recording facility is of particular interest in connection with those black-and-white and color processes in which the composite prints are obtained by photographic reversal from positive sound track and picture films.4-6 The direct-positive sound track thus eliminates the intermediate sound print which ordinarily would be required with such processes. The direct-positive sound track also holds promise in certain television applications where the tonal scale on the television screen is reversed electrically to give a positive picture on the film.
* Presented October 26, 1948, at the SMPE Convention in Washington.
AUGUST, 1949 JOURNAL OF THE SMPE VOLUME 53 149