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

60 PRINCIPLES OF CINEMATOGRAPHY A B C D E Fig. 20.— The Bell & Howell "Shuttle gate" intermittent. entire cycle of operations. The gate and film therein are oscillated bodily in a horizontal direction, so placing the film alternately in contact with the fixed pilot pins and the claw mechanism. The general arrangement of the mechanism is shown in Figure 20. The main aperture plate 'F' supports two pilot pins, numbered tV and '3', one above and one below the exposing aperture. These pilot pins are rigidly fixed to the main plate and do not move. The claw pins, of which there are two, one to enter the perforations on each side of the film are shown at '2'. These pins oscillate in a purely vertical direction as indicated by the arrows. The film is guided through the gate formed by two highly polished metal plates, relieved over the picture area to avoid the possibility of scratching the negative. This gate oscillates in a purely horizontal direction. The action of the mechanism is therefore as follows: The film gate, as shown at 'A', Figure 20, has just moved to the left, and the film is located upon the pilot pins. The 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 an upward direction. It is during this part of the cycle that the film is exposed. The claw pins complete their upward movement and the gate then moves to the right as seen at 'C\ so transferring the film from the pilot pins on to