Richardson's handbook of projection (1927)

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MANAGERS AND PROJECTIONISTS 644 lamp In front of the lens and look through the other way. At least one projector manufacturer, the Power's, places a small battery lamp inside the mechanism, which may be temporarily lighted while framing. No matter what plan be adopted for accomplishing the purpose, however, the picture should never be projected to the screen out of frame. Such work is crude in the extreme, and brands the projectionist as a very slip-shod, careless workman, except possibly in one projector installation where threading must be done in the absolute minimum of time. GENERAL INSTRUCTION NO. 22— REVOLVING SHUTTER.— The revolving shutter is an extremely important and integral part of the optics of the projector. Its function is to close the lens, or, in other words, to cut off the light from the screen during the time the intermittent movement is acting and moving the film over the aperture. It is absolutely essential to intelligent work that the projectionist have a complete understanding of all those various things relating to and connected with the revolving shutter. To begin at the beginning, there is no such thing as a "moving picture," or a "motion picture." What we term moving or motion pictures, is really nothing more or less than the display of a series of snapshot photographs, taken at the rate of sixteen or more per second, and displayed to us so rapidly that one photograph blends into the next, thus forming the optical illusion of motion. Beginning at a frame line between two pictures, measure one foot of film, and you will find thereon precisely sixteen complete pictures. Except in the matter of size these pictures in no way differ from ordinary snapshot photographs. They are presumed to be taken at the rate of sixteen per second, but as a matter of fact in modern practice the speed of taking very frequently exceeds this considerably. As the film passes through the projector these photographs are, by means of the intermittent mechanism, successively posed over the aperture, and while so posed are projected, one after the other, to the screen. The purpose of the intermittent movement of the projector is to pull the film down across the aperture precisely three-quarters of an inch, and to leave it over the aperture for an infinitesimal period of time. At the rate of sixty feet of film per minute, the time each picture remains over the aperture is one-sixteenth of a second, less the time it requires to move the film down, which ordinarily,