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.
HEAT PROTECTION OF MOTION PICTURE FILM By E. D. Tillyer
ALL films used in motion picture projection contain organic materials which will be damaged or destroyed by excessively high temperatures. This applies both to the inflammable and to the noninflammable films; the difference is mainly the kind of damage. One type of film may stand a little higher temperature before damage than another, but both are within what might be called the easily damaged zone.
The heat reaches the film in two ways: first, by conduction and convection; and second, by radiation. In a well-designed machine, this first source of heat should be entirely negligible and is small in almost all machines. The second, radiation, is the source which causes the most damage to the film and is the more difficult to control.
Any ordinary source of light, such as an arc, or concentrated filament tungsten lamp radiates energy of all wave lengths: that is, some short waves (ultra-violet); some longer as the violet, blue, green, yellow, orange, and red of the visible spectrum; and some still longer, known as the infra-red or heat rays which, when strongenough, manifest themselves as heat to the back of the hand or face. No matter which one of these wave lengths falls upon the film, if it is absorbed by the film (i.e. the film is a title or black,) it will appear in the film as heat energy. The only useful part of this energy is in the visible, all the rest is waste energy and objectionable.
If we consider only the visible part of the spectrum, having removed theoretically all the rest, we find that certain parts of the visible appear brighter to the eye than other parts, even when there is the same energy in each part. This region of maximum sensitivity of the eye is in the green at a wave length of 0.55 microns to 0.56 microns, and would be the ideal region for use in projection of "black and white" pictures where protection against heating of the film is desired above all else. Of course, the "white" parts of the film would be green, and absolutely no other colors could be shown. For this region of the spectrum one lumen is 0.0015 watts, or a uniform point source emitting one candle of wave length 0.55 microns to 0.56 microns would require only 0.02 watts. Consequently, if all this energy were absorbed by a film we would have a heating of the film by one candle to the same temperature as it would be if electrical energy of 0.02 watts were put through a resistance in the film.
If we could find a source of light which emitted only monochromatic energy of this wave length (0.55 microns), we would have a source 100% efficient in the production of light, and consequently 100% efficient in keeping the film cool. This light would be fifty
137