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±0.040
4-0.020
U 0.000
2 D
P -0.020
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4 0.04 0
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0.000
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CONDITION A
NUMBER OF PROJECTIONS
NUMBER OF PROJECTIONS
Fig. 17. Projection history of film as measured by changes in the point of best focus. If the point of best focus is determined for each projection of the film, the resulting curves can be related to film performance. This is particularly valuable for preliminary rapid testing to predict film behavior in the trade. A slow rate of change of focus, as in Condition A, is typical of good screen quality; a rapid rate of change of focus as in Condition B is always accompanied by poor image quality on the screen.
then compared with the older in a test with film itself, projected under normal conditions. This film comparison is the final evaluation of the screening done through the semiquantitative use of temperature-sensitive phosphors.
Confirmatory Film Testing
For the proper evaluation of projection apparatus by film testing, it is essential that the work be done with care, especially to insure that due account is taken of the severest possibilities and that the results can be interpreted practically without qualification.
Two procedures for the film evaluation of projection equipment have been
described previously1: (1) the projection of experimental film, designed to provide permanent indication when its critical temperature has been exceeded, and (2) the projection of regular cine positive, under conditions where its focus changes with repeated projection and its variations in image quality can be determined. For either of these tests to be meaningful, it is important that the film be freshly processed and that it not have been projected previously (such previous projection makes the film less critical and there is danger of an over-optimistic evaluation of the equipment). It is also necessary that the print include areas of adequate density, and that it be sharp
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May 1954 Journal of the SMPTE Vol. 62