Journal of the Society of Motion Picture Engineers (1930-1949)

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A Fast-Acting Exposure Control System for Color Motion Picture Printing By JOHN G. STREIFFERT An illuminating system in a contact-printer for color motion pictures is described. Light from a single lamp is divided into three beams which are independently filtered, controlled in intensity, and projected onto the printer aperture. Intensities of the red, green and blue components of the exposing light are measured continuously and photoelectrically and compared with reference voltages which are the analogs of the desired intensities and which are controlled by a perforated tape according to the predetermined requirements of each scene to be printed. Any errors between measured intensities and desired intensities, i.e., between photocell outputs and reference voltages, are amplified and applied to servomotors which rotate vanes in the respective beams until the correct intensities are established. A response time of the order of 1/50 sec has been achieved, and the intensity of the printing light is substantially independent of lamp current and age. A manual control on each of the reference voltages provides for emulsion-to-emulsion variations in print stock. .xTLN ILLUMINATING system in a continuous contact printer used for making motion picture color prints must fulfill many requirements. The more difficult requirements to attain are: 1. Sufficient illumination to expose the color positive material at a printing speed of at least 100 fpm. 2. Provision for control of exposure and/or color balance to compensate for scene-to-scene variations in negative density and color balance and for emulsion-to-emulsion variations of the positive material. The change in ex. Communication No. 1517 from Kodak Research Laboratories, a paper presented on October 8, 1952, at the Society's Convention at Washington, D.C., by John G. Streiffert, Eastman Kodak Co., Kodak Park Works, Rochester 4, N.Y. posure or color balance should be made in a sufficiently short time so as not to be perceptible in the projected picture. Ideally, this change should occur within the frame line. In practice, an operating time of one frame is considered satisfactory, provided there is no overshoot in the system which would cause one frame to be noticeably lighter than adjacent frames. In addition to these two requirements, it is desirable that the exposure and color balance be substantially independent of the operating voltage and the age of the lamp; that the power consumption of the light source be moderate; and that the optical, electrical and mechanical elements of the system be simple and reliable. An optical and exposure control 410 November 1952 Journal of the SMPTE Vol. 59