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May, 1930] CAMERA MECHANISM 539
Darling, Williamson, Prestwich, and Proszinski are some of the names associated with what I designate the claw movement.
Darling used a claw which was driven by two equal cog-wheels geared together and consequently running in opposite directions. To a crank on one of the wheels a claw was pivoted and a prolongation from the bar of the claw carried a curved slot in which a crank pin on the other wheel rotated and traversed from end to end. The combination of movements produced the D shaped path through which the claw pin travelled.
Williamson's movement had only one crank which was pivoted to the end of the claw rod. About the middle of the claw rod was a curved slot which slid on a fixed pin and the claw was caused to take a D shaped path.
In the Prestwich movement the claws themselves were fixed on separate springs, and, had the springs not been stressed at one part of the movement, the claws would have described an oval path; a flat plate was provided just above the film, against which the springs pressed when they entered the film and following the direction of the plate the under part of the oval was altered into a straight line, thus forming a D. These three movements were not pure pin joint movements as they all contained slides.
Proszinski about this time patented a claw movement to some extent like Williamson's but in place of the slide working at the middle of the claw bar, a rocking link caused the middle of the bar to follow a path comparable to that of Williamson's movement. The form of the D produced could not be made quite so perfect but was sufficiently accurate to drive the film efficiently. This was a true pin joint movement having no cams or slides.
The two sprockets and the tension take-up had now become general in cameras, and the lengths of film usually accommodated were from 100 to 200 feet. Perforation had improved to a great extent, but had not reached our present pitch of accuracy, and although the steadiness of the picture had improved considerably, the condition was not what we, at the present time, call steady. About this time the pilot pin was added to the perforator and, for the first time in the history of moving pictures, we had steadiness. Celluloid is a very unstable substance as we all know. Before the addition of the pilot pin to the perforator, considerable variation in pitch resulted. This, combined with the fact that there was no recognized standard, either of width of film, size or shape of perforation, or distance apart of perforations