We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
524 RI( HARDSON'S BLVEBOOK OF PROJECTION
either pass through the light beam, the light will be interrupted at the frequency with which sprocket holes (or dividing lines, as the case may be) pass through the point of focus. A loud hum or "motor-boating" in the sound will result. (26) This can be cured by adjusting the lateral guides until it is no longer heard. An observer in the theatre is necessary if the adjustment is to be made with the greatest accuracy, since a slight trace of such noise will not be heard by the projectionist above the noise of his machinery, although loud enough to annoy the audience.
The most perfect adjustment of the lateral guides is secured by placing a piece of blank leader in the projector and photographing the exciting light upon it. An exposure of from 30 seconds to one minute will leave a thin black line on the blank film. The drive should then be turned to move the film about six inches, and another exposure made. Four or five such exposures will reveal very accurately whether the film is out of adjustment laterally with respect to the exciting light. After the guides have been re-set the light must be photographed again, and so on, until a perfect setting is obtained and the guides are locked into place.
(27) It is necessary to guard against the slightest vibration of any part of the light system. If the slit in the lens tube vibrates, or the filament of the exciting lamp vibrates, the resulting vibration of the light beam will be heard in the sound as noise. (28) The exciting lamp and its holder should be tested for vibration by tapping them gently with the back of lead pencil, one that has no eraser. The lens tube should be rapped more vigorously with the same instrument, or tapped very gently with the butt of a screw-driver. The photo-electric cell and its amplifying tubes, if any, should be tapped softly with the side of a pencil. Any noise heard in the sound as a result of these tests means that the part in question is subject to vibration and must be tightened accordingly, or replaced.
The current supply to the photo-electric cell must be