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A CONTINUOUS TYPE TELEVISION FILM SCANNER* PETER C. GOLD MARK**
Summary. — A motion picture film scanner, the first of the continuous type to be used for television transmissions, is described. The apparatus was put into operation in New York City in the summer of 1937 and has been in use since. In its preferred form the scanner projects the image of a continuously moving film onto the cathode of a dissector tube. Five images, representing different portions of the film in the gate, produced by five stationary lenses, are superimposed one on top of the other, while a rotating shutter with concentric slots permits only one lens at a time to produce an image. The scanning is accomplished partly by the uniform motion of the film and partly by the magnetic scanning of the electron image in the opposite direction. The pictures thus obtained are completely free from shading, cover a great range of contrast, are free from flicker, and are steady. The construction of the scanner is simple and inexpensive.
While the Iconoscope is the best device known at present to pick up scenes where the amount of illumination is limited, the same tube is not the best for the transmission of motion picture films. Devices like the scanning disk, dissector tube, projection type cathode-ray tube, etc., will produce pictures of greater contrast and freedom from the shading effects that represent one of the greatest disadvantages of the Iconoscope. Film scanners which project a continuous visual image onto the Iconoscope or onto a dissector tube have been suggested and are in use. However, they all involve rotating parts such as lenses or mirrors, these parts in some cases numbering as many as forty-eight, which must be preadjusted with extreme accuracy, making subsequent corrections at the projector nearly impossible. Jt was therefore desirable to develop equipment in which the optical elements involved would be stationary and few in number.
Another requisite for such a film scanner is that the film should move through the gate with constant speed instead of with jerky motion, as it does hi the intermittent type of projector, so that the
* Presented at the 1939 Spring Meeting at Hollywood, Calif. ; received April 7, 1939.
** Columbia Broadcasting System, New York, N. Y.
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