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EVOLUTION OF PROFESSIONAL CAMERA
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The shrinkage characteristic of the film, which is the term used to define the alteration in length and width to which the film is subject during its laboratory processing, brought forth the necessity of painstaking investigation before the shape, size and pitch of its perforations could be standardized.
Shrinkage, incidentally, necessitated the development of perforating machines of extreme precision of operation; and that of sprockets for cameras, printers and projectors in which the shape, size and pitch of the teeth were carefully calculated.
It is noteworthy to mention that the European method of counteracting the ill effects of film shrinkage consisted in the establishment of two dimensions of film perforations: one for unprocessed negative film, and one for positive film, in order that the latter would coincide with the reduced dimensions assumed by the negative film after processing.
American ingenuity, however, could dispense with this rather bothersome method. A. S. Howell lead the way by designing the mechanism of the printing machine in such manner that a compensation for the differences in dimension between processed negative and unprocessed positive films was obtained automatically and with greater accuracy than was possible through the use of two perforations of different size.
The shape of the perforation for negative film was officially standardized by the Society of Motion Picture Engineers after the Bell & Howell Company of Chicago had produced the perforating machine
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Fig. 3 Standard dimensions of 35mm. film. A — Bell & Howell negative perforation. B — Rectangular positive perforation. Below, enlarged view of shape and dimensions of both perforations.