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Proposed American Standard
Dimensions for
35mm Motion Picture Short-Pitch Negative Film
PH22.93
Appendix 1
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 dies. 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.
Appendix 2
Most motion picture film is printed on sprocket-type printers. Maximum steadiness and definition are secured on a sprocket-type
P. 2 of 2 pp.
printer when the negative film is somewhat shorter in pitch than the positive stock.
For many years, this difference in pitch has come about due to shrinkage of the negative film base on processing and aging.
There are currently becoming available new low-shrink film bases which do not shrink sufficiently to provide the necessary pitch differential between negative and print stock for proper printing on sprocket-type printers. This standard is intended to give dimensions for perforating low-shrink film material so that it will have, as nearly as possible, optimum dimensions at the time of printing.
For the purpose of this specification, lowshrink film base is film base which, when coated with emulsion and any other normal coating treatment, perforated, kept in the manufacturer's sealed container for 6 months, exposed, processed, and stored exposed to air not to exceed 30 days at 65 to 75 F and 50 to 60% relative humidity and measured under like conditions of temperature and humidity, shall have shrunk not more than 0.2% from its original dimension at the time of perforating. The final measurement should be made after conditioning the film for 24 hours to a humidity of 55 — 5%.
This definition of low-shrink film is to be used as a guide to film manufacturers, and departure therefrom shall not be cause for rejection of the film.
NOT APPROVED
534
December 1952 Journal of the SMPTE Vol. 59