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December, 1950 cricks : engineering aspects of film production
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reached a high state of perfection in the film " Rome Express." For recent developments, much credit must be given to the Independent Frame process above-mentioned.
For this process equipment of very special design has been evolved. The arc lamp is capable of carrying currents up to 300 amperes ; through an optical system of novel design, its light is condensed upon the film or transparency, which is cooled both by air and water.7 The objective lens is movable by remote control laterally, vertically, and, for focusing, longitudinally ; the object of remote control is to enable the picture to be focused and positioned on the screen by an operator standing near the camera, and able therefore to match the background with the already positioned foreground set. The moving background projector is arranged to run forwards or backwards, so that at the end of a take the film can be wound back, ready for the next take.8
IV— PROBLEMS OF PICTURE STEADINESS.
â– Ultimately, the acceptance by the viewer of the illusion of reality depends upon the steadiness Of the projected image, and upon' its critical sharpness of focus. In order to achieve an adequate standard of steadiness, it is essential that
Fig. I. Principle of Process Projection. The projector is to the left, and the camera on the right photographs the foreground set with the image projected upon the translucent screen.
the accuracy of registration of the image — not merely of the film itself — in the projector gate should be of the order of two to three mils ; an error of this order is equivalent to a picture movement on the screen of from a quarter of an inch to one inch. With the wide-aperture lenses now used, both in cameras and projectors, the film must not depart by more than one or two mils from the focal plane of the lens.
Summation of Errors.
These tolerances represent the summation of a number of possible errors. From the negative a master positive or " lavender," is printed, and from this a dupe negative from which the release prints are produced. The travelling matte and back-projection processes just described are in effect duping processes, in which, however, the standard of steadiness is even higher than that in other processes, because of the noticeable effect of background unsteadiness in relation to a steady foreground. In addition, the making of " opticals " introduces for part of the footage yet another duping operation.
It will be seen that from the original photography to the projection of the film in the kinema, there is a sequence of at least four, and more often six or eight, films. Our permissible error of two or three mils represents, therefore,