The handbook of motion picture photography (1927)

T 11 E HAN I K ( ) F M olio N film from the uppo spool, then some -lack or a "loop" as it is technically known, the intermittent, the second loop, the second sprocket and then the take-up reel. The first cameras had two sprockets, one to take film from the ivvd reel and one to take the film from the intermittent. It is obvious that should anything occur to disturb the synchronism of the two sprockets that either one of two things would happen. The lower loop would be lost and the film would be stripped through the gate, ruining the film and probably damaging the intermittent mechanism. If this did not occur the lower loop would be enlarged until the camera chamber would be clogged with film. In fact, these things did occur so constantly that the two sprocket system was changed to the master sprocket system. In this system the film is pulled from the upper spool by the top of one large sprocket, while the film is taken from the lower loop and fed into the take-up spool by the bottom of the same sprocket. In this manner synchronism is made positive. All cameras which make any pretentions to quality now use the master sprocket. When the film leaves the lower side of the master sprocket, some means must be provided to take up this film. An ordinary drive will not suffice. When the film first starts the diameter of the spool axle is roughly one inch. Thus about three inches of film are taken up with each spool revolution^ When the one-hundred foot spool is almost full the diameter is almost four inches, taking up about one foot per revolution. As the film must be kepi under moderate tension between the lower sprocket and take-up spool, 54