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

July, 1939] A TELEVISION FILM SCANNER 23 and the brackets holding the lenses are permanently clamped down. With this method coincidence of the five images can be obtained accurate to within a fraction of the width of a line both in the horizontal and the vertical directions. It is, of course, necessary that the film running continuously through the projector be steady within these limits. However, suitable mechanical filters make such uniform film speed possible. There is one more important consideration in this film-scanning method that requires close attention. The distances between centers of the five dissecting lenses in the vertical direction correspond to certain distances between successive film-image centers on the film. FIG. 5. Diagram of complete telecine channel employing the projector. At any distance between the plane of the dissecting lenses and the cathode of the pick-up tube sharp focus of the film picture together with most accurate coincidence of the five images must be available. However, it is known that there are rarely two reels of film that exhibit the same shrinkage, that is, the same spacing between centers of successive images. A method had to be developed whereby the system could be quickly adjusted for any shrinkage while maintaining good focus and coincidence over the entire image. It has been determined experimentally that the shrinkage of film will vary anywhere between 0 and 12 mm per 50 frames, which corresponds roughly to from 0 to 0.8 per cent. A large number of test-reels with suitable patterns, each of which showed different shrinkage between the limits