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

GENERAL PRINCIPLES 25 distance equal to one picture. When this has occured pin 'C will be just leaving the slot 'G' as seen in Figure 3d. The condition when the pin is in the process of moving the pictures forward is shown in Figure 3c. By this means it was possible to advance the picture-carrying-disc intermittently and yet to continually rotate the operating handle. Particular note should be taken of the intermittent mechanism just described since it forms the basis for many modern motion picture projector mechanisms. With the introduction of photographic emulsions coated on transparent film support the progress towards modern cinematograph cameras and projectors became rapid. Two improvements were immediately available, the first being that a much greater number of pictures could be taken on a roll of film than could be mounted on a circular disc. The second feature was that the film could be easily rolled up and stored. Although the earliest attempts to produce motion pictures on lengths of film were made by driving the film by friction, it quickly became apparent that some more positive form of traction was necessary. The natural development was therefore to perforate holes along each edge of the film and to pass it over wheels carrying teeth in a similar manner to the action of a chain passing over a sprocket wheel. It was from the likeness between these two systems that wheels carrying teeth with which to move perforated film became known as 'sprocket wheels'. Fig. 3. — Early intermittent mechanism.