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Appendix
(This Appendix is not a part of the American Standard Dimensions for 35mm Motion Picture Film— Alternate Standards for Either Positive or Negative Raw Stock, PH22. 1-1953.)
The dimensions given in this standard represent the practice of film manufacturers in that the dimensions and tolerances are for film immediately after perforation. The punches and dies themselves are made to tolerances considerably smaller than those given, but owing to the fact that film is a plastic material, the dimensions of the slit and perforated film never agree exactly with the dimensions of the punches and die:,. Shrinkage of the film, due to change in moisture content or loss of residual solvents, invariably results in a change in these dimensions during the life of the film. This change is generally uniform throughout the roll.
The uniformity of perforation is one of the most important of the variables affecting steadiness of projection.
Variations in pitch from roll to roll are of little significance compared to variations from one sprocket hole to the next. Actually, it is the maximum variation from one sprocket hole to the next within any small group that is important.
Perforations of this size and shape were first de
scribed in the Journal of the SMPE in 1932 by Dubray and Howell. In 1937, a subcommittee report reviewed the work to date. The main interest in the perforation at that time was in its use as a universal perforation for both positive and negative film. The perforation has been adopted as a standard at this time largely because it has a projection life comparable to that of the perforation used for ordinary cine positive film (American Standard Cutting and Perforating Dimensions for 35mm Motion Picture Positive Raw Stock, Z22.36-1947, or the latest revision thereof approved by the American Standards Association, Incorporated), and the same overall dimensions as the perforations used in the negative film (American Standard Cutting and Perforating Dimensions for 35mm Motion Picture Negative Raw Stock, Z22.341949, or the latest revision thereof approved by the American Standards Association, Incorporated). It should be particularly noted that although the present standard has the same overall dimensions as the older cine negative perforation, positioning pins or sprocket teeth made to fit this perforation exactly will injure the corners of the cine negative perforation.
PH22.1-1953
68
January 1953 Journal of the SMPTE Vol. 60
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