Journal of the Society of Motion Picture and Television Engineers (1950-1954)

handling, since the values for the variation in width of film found in exchanges are appreciably greater than we would have predicted on the basis of factory measuremen ts . Note that only 1^% of conventional 16-mm film lies above the ASA line. However, 24% of the 32-mm film exceeds this value, and much of it would be expected to be excessively unsteady. A good portion of this variation presumably is controllable because there is a difference between laboratories, as shown in Fig. 5. Accordingly, it is reasonable to hope that the laboratories having the wider spreads can reduce them to the narrowest spread observed. (A demonstration reel was projected which showed the unsteadiness of the screen image produced by variations in width of different extents. It was pointed out that the 16-mm pictures were not made from 32-mm film, but were selected from an unofficial museum of defects kept for the purpose of eye calibration.} A certain need for improvement in the dimensions and consequently the behavior of some 1 6-mm film made by the 32-mm process is made clear by these measurements. The procedure by which improvement is to be obtained is not so clear. Proposals have been made to the Standards Committee of the Society for a standard describing 16-mm film made by the 32-mm process. The proposal was not entertained because most of the members of the Standards Committee felt that it did not matter how the film was made. Indeed the user need not, and may not, know how the film is produced; therefore, the film should meet the appropriate ASA specifications. In view of the fact that this specification is lenient, it actually devolves upon the purchaser to assure himself that the film is as good as he bargained for. Maximum Width of Film The maximum width of the film is a dimension of interest.7 Film which is too wide may not perform well in projectors made to close tolerances, or in projectors operating under conditions where the film has swollen because of the prevailing high humidity. Let us see what variation is encountered in raw film. Figure 6 shows in the upper graph the variation in the maximum width of the film as it is made. The narrow spread is due in part to the fact there is no difference in age. Lest someone feel skeptical about the graph, let it be said that the range in width of film seldom exceeds 0.0010 in., and that the variation in width for any one strip is generally much less than that. The lower graph shows how various lots of unexposed negative film, made between 1941 and 1950, varied in width. Variations in age and storage conditions increased the spread in dimensions. In Fig. 7 is shown the distribution of the slit width of film made during one month of factory production. The horizontal scale is spread out thirty times wider than in Fig. 6, thus showing that there is the Gaussian, theoretical distribution shape that one expects. In Fig. 8 the upper chart shows the maximum width of 16-mm film made from 32-mm film. The lower chart shows the width of 16-mm film made from 16-mm factory-slit film. The amount of oversized 16-mm film made from 32-mm film is small, but real. This is a quantity which should be taken into consideration when designing equipment which is to operate with all available films and under all conditions, including those of high relative humidity. Figure 9 shows what we think the width of the films of Fig. 7 would have been when freshly processed and conditioned to 90% relative humidity. The first correction was made by estimating what the width after processing would have been, from the shrinkage values observed in the exchanges. This value was then further increased by the appropriate amount to give the effect of conditioning to 90% relative humidity. 408 November 1951 Journal of the SMPTE Vol. 57