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CHAPTER 13
16-mm SOUND-FILM PROJECTION
In recent years the growth of 16-mm cinematography has been so rapid that modern sound projectors have come to resemble 35-mm professional machines much more closely than those relatively simple and earlier silent mechanisms from which they have been developed. Although the complete mechanism is now quite a complicated and highly accurate piece of engineering, it still depends upon the basic systems of film traction which have been the fundamental requirements of all motion picture apparatus for many years. These requirements are identical with those necessary in camera mechanisms and are briefly re-stated as follows: (1) That the film shall be drawn from a supply spool at a constant rate and, after passing through the machine, shall be fed to the take-up spool at a similar rate. (2) That the film shall be formed into a free loop between the points of supply and take-up so that intermittent motion may replace the constant forward motion over a small section of the film path. (3) Assuming that the film may be guided through a channel over a portion of the path where intermittent movement occurs, an aperture must be so formed in this channel that one image on the film is accurately 'framed' and may be projected onto the screen by a suitable illuminating and associated optical system. (4) Since the film will be caused to come to rest in the guiding channel whilst projection is in progress, and will then be rapidly moved forward in order to bring the next frame into correct alinement, a continuously rotating shutter must be provided so that light is only allowed to pass to the screen when the film is stationary in the projecting plane and so that the forward movement of the film from frame to frame is masked from view.
Basic Arrangement of the Silent Projector
The basic arrangement of the mechanism necessary to project pictures and, therefore, what might be termed the 'silent' projector
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