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180 HANDBOOK OF PROJECTION FOR
heading "Lenses," beginning at page 125. We will provide you with the necessary charts and diagrams, by the application of which you will be able to so adjust your projector optical system that maximum results will be had, both in brilliancy and evenness of screen illumination, and, what is almost equally important, they will be had at maximum efficiency.
It must be remembered, however, that where local conditions vary so widely, even the most carefully calculated and prepared formula is likely to in some measure fail of its highest purpose unless it be applied with intelligence and understanding. It is for this reason we urge projectionists to study and come to an understanding of the underlying principles which govern in the selection and adjustment of the projector optical system.
It is a deplorable fact that the lack of such understanding on the part of projectionists, coupled with the failure of condenser lens manufacturers to provide proper lenses and the failure of theatre managers and exhibitors to purchase optical equipment of the right design and quality, has, ever since the very inception of motion picture projection, not only caused a literally huge waste in light, which means a waste in electric energy, but has also made it impossible to exactly duplicate the illumination of all points of the film photograph upon the screen, without which it is impossible to secure the same apparent depth in the picture which the natural scene presented to the "eye" of the high grade camera lens, and which was by that lens impressed faithfully upon the film.
It has often been remarked that the same photoplay has an apparently increased stereoscopic effect, or perhaps we might better say a greater "depth" in one theatre than in another, and this has been placed to the credit of the screen, whereas the real credit was not due to the screen at all, but to the correct selection of the various elements of the optical system and their correct adjustment with relation to each other, so that the film image was evenly illuminated and the evenness of illumination was faithfully transmitted to the screen.
One of the big outstanding facts in projection is that evenness of illumination is absolutely essential to perfect results on the screen, and evenness of illumination at the screen is impossible unless we first secure evenness of illumination of the film photograph at the aperture, and then project the