Journal of the Society of Motion Picture and Television Engineers (1950-1954)

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Fig. 6. Close-up of picture film trap, showing method of threading film. worm and gear H and G and the manual indexed control I. The pair of epicyclic gears have different gear ratios and in consequence, when the carrier is rotated about the jack-shaft center, the sound film is advanced or retarded with respect to the picture film. Film Traps Figure 6 is a view of the picture-film trap and gate and illustrates the method of threading. The film is held between the two hands and laid in the film trap under light tension to sense the engagement of the sprocket teeth with the holes. The thumb is then in a position to press the film down and operate a trigger but ton shown at A which causes two filmretaining slides to move over the edges of the sprockets and retain the film in engagement. One of these slides may be seen as B. Closing the gate F completes the threading. The latter is held closed by the lever G, which may be operated at any time to release the gate but not the film-retaining slides. This permits ready access to the full area of the film for marking without losing synchronization. Depressing the upper lever C opens the gate and releases the film simultaneously. For synchronizing purposes, the handwheel is turned to index any one frame with a reference arrow located in the 322 September 1953 Journal of the SMPTE Vol. 61