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MANAGERS AND PROJECTIONISTS 638
mass on the polished surface of the tension shoes, which, besides causing the tension shoes to jump and clatter, is likely to injure the film itself more or less seriously.
When using a first run film, the surface of the tension shoes and the aperture plate track should be carefully examined after each reel, (excess of film cement will sometimes deposit on the tracks of the aperture plate) and any deposit found thereon must be carefully removed.
BEST WAY TO REMOVE DEPOSIT.— The deposit may be removed by scraping it off with the edge of a silver coin, or by the use of some other soft metal, but the best way is to use a wet cloth. Water softens the emulsion instantly, therefore the deposit may be quickly washed off without any possibility of injury to the polished parts.
CAUTION. — Never use a knife blade, screw driver or other hard steel instrument to scrape deposit off the tension shoes or aperture plate tracks, because by so doing you will scratch the polished surface and thus increase the tendency to deposit.
Many plans have been tried for the elimination of this trouble, but the only really practical thing is the lubrication of the film track.
It is possible to make a fairly effective film track lubricator as per Fig. 77-C, Page 274.
It is even possible to reduce the trouble somewhat by rubbing the tension shoes with the end of a tallow candle before threading the projector, or by holding a tallow candle lightly against the teeth of the upper sprocket occasionally for a few seconds while the film is running.
GENERAL INSTRUCTION NO. 11— WORN APERTURE PLATE TRACKS. — In instruction number 9, we said that one of the offices of the gate tension is to hold the film perfectly flat over the aperture. This, of course, cannot be done unless the surfaces of the aperture plate tracks be themselves true and level; it therefore follows that excessive wear of the aperture plate tracks may, and probably will, cause a buckling of the film over the aperture, and an out-of-focus effect on the screen. By this we do not wish to be understood as meaning that buckling of the film over the aperture is always due to this cause, but while it may be induced by other causes, such as old, shrunken film, worn aperture plate tracks are pretty sure to produce the trouble. Buckling of the film over the aperature will cause an out of focus effect or an "in and out" of focus effect.