International projectionist (Jan 1963-June 1965)

Volume 38 August, 1963 Number 8 FILM SHRINKAGE AND FRAME REGISTRATION By ROBERT A. MITCHELL Improvement in the rocksteadiness of theatre motion pictures during the past few decades is due in great measure to improvements in the aging characteristics of the film, itself. Other refinements in the art which have exerted a decidedly beneficial effect upon the quality of professional projection include more accurate camera and projector intermittents, improvements in film processing and printing, the use of film stock perforated by the manufacturer instead of by the studios and laboratories, and a better understanding of optimum storage conditions for all the different types of film stock in use. As far as theatre-release positive film stock is concerned, the substitution of high-acetyl acetate safety film for the relatively unstable and dangerous nitrate film formerly used has been a significant factor because of the relatively low and comparatively uniform shrinkage of triacetate base. The film shrinkage problem still exists, of course, because all known cellulose-ester plastic materials shrink to some extent with time and upon exposure to varying conditions of heat and moisture. The film processer worries about the difficulties resulting from the stretching and shrinking of film in his developing and drying machines. The special-effects man is concerned about the rocksteady superposition of mask films. The color lab technician is likewise concerned with the registration of his three color separations, and in black-and-white work with the bad effects resulting from negative shrinkage. And the projectionist has anxieties of his own: variations in the normal shrinkage of the positive print films he projects will cause unsteadiness of the pictures on the screen. Film is Perforated Accurately Assuming that all camera, printer, and projector units are correctly designed and maintained in top-notch operating condition, the accuracy with which the succeeding frames of a film are registered, one after another, is determined by the accuracy of the perforations punched in the margins of the film. Shrinkage of the film stock alters the "pitch," and if the shrinkage is irregular, the accuracy, of the perforations. When film shrinkage disturbs the accuracy of frame registration in printing or projection, the bad effects result directly from ensuing inaccuracies in the pitch of the perforations — the distance from the edge of one perforation to the corresponding edge of the succeeding one. Film is perforated accurately by the manufacturer, the errors in pitch, if any, being well below the 0.00015inch tolerance specified by the American standards for perforations in 35-mm motion-picture film stock. This statement probably applies to all the leading brands of film, European as well as American. It would not be an easy job to discover any inaccuracies in the perforating job done by the film manufacturer, and would be impossible if the film samples had been processed, used, or stored for any length of time. Check-tests on perforation accuracy must be made on unprocessed raw stock immediately after it is perforated, and under the same conditions of temperature and humidity maintained in the perforating rooms. Such check-tests are made at frequent intervals by the film International Projectionist August, 1963