Film Scanner for Use in Television Transmission Tests

This paper describes the design and construction of a television film scanner primarily intended for use as a testing tool in designing circuits suitable for television program transmission. The equipment employs electronic scanning and the image dissector is used as the electronic pickup device. The image dissector has a high degree of linearity between light input and signal output and the picture signal is not accompanied by any spurious shading signals. Furthermore, the direct-current component of the television signal is directly available at the output of the tube. The lower sensitivity of the dissector tube is not important in this case since a highly efficient optical projection system makes it possible to override noise to a high degree. In film scanners for entertainment purposes it is desirable to use ordinary 24-frame motion pictures and such film scanners therefore include a mechanical or optical translating mechanism for translating the 24-frame film picture into a 30-frame interlaced television picture. In the present equipment it was found more expedient to simplify the construction by allowing the use of specially printed film. Ordinary 24-frame film is "stretched" by printing every other frame twice and the remaining frames three times in succession, thereby producing a film with a total of 60 frames instead of the original 24. Vertical scanning is then obtained by the continuous motion of this film at the rate of 60 frames per second and horizontal scanning by a simple electronic line sweep in the dissector tube.