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June, 1931] CONTINUOUS PROJECTORS 713
when the film photographs are in synchronism with the prisms, the registration of the successive images on the screen will exactly equal that to which the prisms were adjusted or indexed, assuming the film to be perfect and the motions of the film and prism-wheels to be uniform.
The registration will therefore be seen to depend upon radically different factors from those of the intermittent projector. These factors are:
(1) The registration of the compensating elements, which may be adjusted or indexed with extraordinary precision and which cannot get out of adjustment or vary because of wear.
(2) Uniform motions in the compensating wheels. The law of inertia tends to keep these motions uniform, and wear in the gears should not affect the uniformity of the motions.
(3) Uniform motion in the film. With a friction drive this is also unaffected by wear. A moderate amount of wear in a sprocket would tend to reduce the high-spots and make the teeth more even.
(4) Synchronization.
The advantages, derived from the mechanical features and the principle of the registration, may be summarized as follows:
(a) A higher order of precision.
(6) A more uniform and longer sustained accuracy.
(c) The mechanism has fewer parts and is of the heavy-duty type.
(d) Oiling nuisance is avoided, and the sound track and picture surfaces are kept free from oil.
(e) Noiseless operation.
(/) Freedom from vibration, as all the moving parts are balanced and revolve uniformly.
(g) Momentum of prism-wheels tends to overcome certain inaccuracies in the mechanism.
(h) Momentum of the film overcomes many inaccuracies in the perforations.
(*) Wear on the film has less effect on the projection.
(j) Momentum of film prevents sudden lateral movements.
(k) Elimination of tension shoes possible, as a loose loop of film can be made to press itself with sufficient flatness against the aperture plate.
(/) Elimination of tension shoes makes possible the use of raised or embossed margins on the emulsion side of film, thus forming an air space and preventing scratches on the sound track and picture surfaces when wound up.
(m) Absence of tension shoes eliminates the effects of variations in the thickness and smoothness of the film, and the effects of variations in the "give" or flexure of the film at the perforations when under strain.
(n) Minimum of strain and wear on film.
(0) Fire hazard reduced as there is less possibility of splices parting
(/>) Moving film fans itself, so withstands higher temperatures.