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OPTICAL PRINTING
Lloyd Knechtel*
WITHIN the past few years the motion picture industry has almost universally adopted the system of optical printing in its many and varied uses and forms, and has found it invaluable as both an artistic and an economic aid. Optical printing may be denned as a printing method which produces duplicate motion picture negatives or positives optically rather than by contact. In other words, it is more nearly akin to the still photographer's familiar process of copying than to true printing, for the scene is actually rephotographed from a previously made positive or negative. Perhaps the clearest idea of the process, however, can be gained from a brief description of an optical printer.
In the first place, the optical printer, unlike any other photographic apparatus, usually has its own source of power-supplv — a motor-generator set, generally supplying direct current. This is to assure an even flow of power for the printing-light and driving-motors, free from the inevitable fluctuations that occur if power is taken from the usual studio lines. The optical printer itself is in every case designed to suit the individual requirements of the cinematographer operating it, and built with the utmost precision. In most cases an ordinary lathe bed is used for the foundation, not merely because it offers ready-made the most suitable unit, providing all of the necessary basic adjustments, but because its precision design and rigid construction provide the absolutely solid foundation that is vital in high-grade trick and multiple-exposure work, where maximum steadiness and accuracy are required. The actual mechanism itself consists of two units: a printer-head, or rebuilt camera mounted at one end of the bed, and a regulation photographing camera at the opposite end. Both of these are motor-driven, and their action is mechanically interlocked.
The printer-head is essentially a lensless projector, as it consists of a light-source, an intermittent film movement, and a means of carrying developed film — usually positive. In order to ensure absolute accuracy, however, this intermittent movement is usually either a rebuilt camera, or at least a camera-movement, equipped with registering-pins.
Assuming that the film used in the printer-head is positive, the regulation camera rephotographs this positive while held in a still position by the registering-pins. During this photographing, the shutter on the camera-head is naturally open. Since the movements of the camera and printer-head are mechanically synchronized, when the positive film is being moved on to the next frame, the shutter of the photographing camera is closed, and an unexposed frame therein being brought into place. By this means, since the movements of both the positive film in the printer-head and the negative film in the
•Head of Special Effects Department. R-K-O-Radio Studios.
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