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Standards PH22.5, PH22.12 and PH22.93 Related to 16mm and 35mm Low-Shrink Film
Two REVISED American Standards and one Proposed Standard are published on the following pages for three month trial and criticism. All comments should be sent to Henry Kogel, SMPTE Staff Engineer, prior to April 1, 1953. If no adverse comments are received, the three proposals will then be submitted to ASA Sectional Committee PH22 for further processing as American Standards.
The introduction of safety base of a low-shrink type removes some of the problems of film dimensions but has introduced two slight difficulties. To take care of these difficulties the Film Dimensions Committee has recommended modifications in the dimensional standards for 16mm film (PH22.5 and PH22.12) and has introduced a new standard (PH22.93) for 35mm film to be used as negative material on the sprocket-type printer.
In the case of 16mm film the introduction of low-shrink type base produced an increase in the number of cases where film has jammed in the camera gate. Investigation showed this increase to be due to the fact that many camera manufacturers had produced gates which would pass film only if the width of the film was appreciably less than the upper limit (0.630 in.) of the cutting and perforating tolerance. Now, the lowshrink type of film, even though originally slit within these tolerances, would swell at high humidities just as much as the older type with the result that its width at the time of use might well exceed the tolerance. This trouble
rarely occurred with the older type of film because its characteristics were such that it would shrink enough by the time it reached the camera to compensate for any possible swelling at high humidities. The Committee recommends, therefore, an alternate standard slitting width of 0.628 in. ± 0.001 in. to be used with low-shrink film.
The Committee calls special attention to the fact that the act of writing the standard this way does not represent a decrease in the actual width of film as used by the customer. Manufacturers of apparatus should not use this change in dimension as a reason for changing the width of film gates.
In the case of 35mm film the same reasoning might apply but since no actual difficulties have been reported, the Committee does not wish to make a change in the nominal width of the film. Another difficulty, however, has been introduced. This difficulty occurs only on film which is to be used on sprocket type printers.
It will be recalled that the negative film on a sprocket-type printer must be shorter in pitch than the positive film if the two are to travel together around the sprocket without slippage relative to each other. For most printers this difference in length corresponds to a shrinkage of about 0.3%. Now, the negative film, such as was formerly used when nitrate film base was generally used, would shrink to approximately this value by the time it was ready for making release prints. Not much difficulty was encountered, therefore, arising from the slippage between nega
December 1952 Journal of the SMPTE Vol. 59
527