Principles of cinematography : a handbook of motion picture technology (1953)

302 PRINCIPLES OF CINEMATOGRAPHY ® ® © © © Fig. 134.— Fixed pilot-pins with oscillating gate mechanism. gate then continues to move to the left, as seen at 'B', until the back-plate comes into contact with the shoulders of the aperture plate in this manner the film is clamped rigidly in the gate channel. At the same time the claw pins commence to move in a downward direction. It is during this part of the cycle that the film is exposed. The claw pins then complete their downward movement and the gate moves to the right, as seen at 'C, so transferring the film from the pilot pins onto the claw pins. It is important to note that the nose of the pilot pins projects sufficiently to overlap the nose of the claw pins and, because of this, the film is always under control by one or both sets of pins. The claw pins now move in an upward direction, as seen at 'D\ and so advance the film by a distance equal to one pitch or frame. It should be realised that, in this machine, the 16-mm film travels upwards whilst the 35-mm film moves in a downward direction. The gate then moves to the left, as seen at 'E', and transfers the film from the claw pins once more onto the pilot pins. The cycle is then repeated. The pilot pins are separated by a distance equal to five perforation intervals, or four pictures. It is because of this control over a considerable length of film, and also due to the accuracy with which the pilot pins fit the perforations, that it is possible to dispense with the use of conventional edge guides in the film gate. The film is therefore freely suspended on the pilot or claw pins, except for that part of the cycle during which the gate is closed and the film comes under pressure from the aperture plate. It should be noted