International projectionist (Jan 1963-June 1965)

manufacturer to insure a consistently high quality of product. All film, even triacetate, swells in processing solutions and shrinks upon drying. More important, film normally swells when the moisture-content of the air is high, shrinks when it is low. and keeps on shrinking w ith the passage of time. Old or processed film can pro\ ii U» no clues whatever as to the accuracy of the perforating process. Nitrate Film Shrank Severely Certain samples of nitrate film of very ancient vintage reveal apparent shrinkages in excess of 1', in length, but we cannot he sure that the films in question really shrank so much — we do not know what the original perforation pitch may have been. But we do know that nitrate film shrank much more badlv than modern triacetate stock, and in a more irregular manner. The irregularity of shrinkage is easily discovered l>\ projection with a mechanism specially modified to increase the length of film between the intermittent sprocket and the projector aperture, inasmuch as shrinkage registration errors add up algebraically, sometimes cancelling one another and sometimes stacking. \ all old-timers in the projection craft remember. nitrate film had undergone considerable improvement since the earliest days of the art. Although triacetate film is better in main ways, nitrate was prettv good stuff at the time acetate supplanted it. After five years of storage under good conditions of temperature and relative humidit) I 7!!: F and (>()', Rlli. \ essed positives on the best nitrate stock shrank longitudinal]} about 0.0',. Ordinarv projection use with repeated shipping and storage intervals under diverse conditions undoubted!) accelerated the shrinkage of nitrate and mav have aggravated irregularities in the rate of shrinkage, but unless very old or much abused in use. nitrate theatrerelease prints gave fairlv pood screen results. It is doubtful, however, that the shrinkage characteristics of nitrate release stock would permit this type of film to be used with satisfactory results under modern conditions of high-intensitv widescreen projection, or in large drive-in theatres. For these conditions triacetate stock is preferable. Normal and Low-Shrinkage Acetate Triacetate release-positive film, processed and stored at 7!! F and Oil', KH. shrinks onlv 0.1', in a 5-year period. Continued storage due- not appear to result in appreciable additional shrinkage. Triacetate negative stock shrinks less than 0.2', after 3 years of storage at 78° and 60', RH: and no further shrinkage normallv occurs. The sharpness of modern color-film prints is largely due to the low shrinkage of triacetate negative, for large and irregular shrinkages in the separation masters, duplicate negatives, imbibition positives, etc. might result in misregistrations which would blur the images. Special low-shrink base may not be quite tough enough to withstand the wear and tear and intense heating of the projection process, but it is now nearly always used for duplicating films as well as for camera negative stock to insure rocksteady photographic images in the final prints. Since there are 16 frames per linear foot of standard 35-mm film, the frame pulldown distance amounts to three-quarters of an inch. And with 4 sprocket holes per frame, the standard perforation pitch must be onequarter of three-quarters of an inch, namely. 0.1873" between corresponding edges of two adjacent perforations. In actual practice, however, a slightly smaller perforation pitch has been agreed upon and universally used. International Projectionist August, 1963 B&H DH Fig. I — Shapes of film perforations in present-day use. The B & II < Bell & Howell) perforation, oldest of the jour, is the preferred type of perf. for most negative film. It was also universally used for positive stock until the mid-1920's. and continued to be used for Technicolor prints until about 1950. The KS I Kodak standard) rectangular perforation leas devised by J. C. Jones of Eastman Kodak in 1923, and put into use almost at once for release-print stock. The improved Hearing qualities of the KS perf. is due to the roundei/ corners; and the increased height (from 0.073 inch to 0.078 inch) eliminated the mechanical interference experienced with B & II perfs. in one make oj projector. The 1)11 ( Dubray-Houell ) perforation was proposed in the eurh I930's to provide a long-life perforation which could be used in precision step-printers designed for B & H perfs. The DH perf. was adopted for color prints in 1 '>!(>. and resembles the KS perf. except for a height corresponding to that of the old B & H perf. The CS (CinemaScope) perforation is a reduced-width version oj the Dll per). The use of CS-perforated prints requires the narrow-tooth sprockets now used almost everywhere. This diagram and notes on perforations suggested by "Pin Registration" by A. C. Robertson, JOURNAL OF THE SMPTE, Feb. 1963. "Long" and "Short" Pitches The regular ■"long*' pitch for the perforations punched in all positive stock and some negative and intermediate-film stocks is 0.1870". A special "short" pitch of 0.1866" is also available for negative films. Short-pitch negative gives optimum results in continuous-type printers having curved exposure gates to compensate for the average amount of negative shrinkage encountered in the days of nitrate film. Although the maximum amount of shrinkage encountered in triacetate theatre-release prints is not very great, certainly not much greater than about 0.4%, projectionists have sometimes wondered whether this normal shrinkage is deleterious to the quality of the picture on the screen. The answer is definite: it is not harmful in any way and cannot be perceived on the screen so long as the amount of shrinkage, whatever it may be, is uniform. Neither will there be any mechanical difficulties in the running of the film. The 0.943" — ■ and 0.945" — diameter intermittent sprockets in general