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MANAGERS AND PROJECTIONISTS 1057
The Exciting Lamp
NOTE. — This applies equally well to all makes of sound-on-the-film apparatus.
THE exciting lamp (also by some termed the '' sound lamp") is the light source supplying illumination to or for the film sound track in the motion picture projector sound pick-up system. It is imperatively essential to good results in sound reproduction and projection that the illumination it supplies be steady, and of exactly the correct value, which latter is gauged by the amperage flow through its filament.
Let it be clearly understood, however, that passing the correct current flow through the lamp filament will not insure good results unless the lamp itself is in perfect condition, nor will good sound results be had with a perfect lamp and correct amperage unless the slit optical system, which includes all lenses between the light source and film, be in correct adjustment, clean, the light correctly adjusted upon the slit and properly focused upon the sound track. In addition to all this it is essential that the image of the slit be correctly centered sidewise upon the sound track, so that it will not extend either into the picture portion of the film or into the edges of the sprocket holes.
Further along I shall advise you how to make a practical test for sidewise centering of the slit light for Movietone film.
To summarize, the following requisites are essential to perfect results: (a) That the exciting lamp itself be