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.
Interference coatings are deposited on reflectors in a 60 inch vacuum chamber under rigid instrument control and with constant monitoring by technicians.
Individual finished reflectors are checked for light reflecting and heat transmitting qualities as well as for beauty in appearance.
some time. They reduce aperture heat to about 55% of its original value when an ordinary silvered reflector is used in the lamp, but it should be remembered that some of the heat elimination is the result of eliminated, and thereby wasted, light.
Interference filters do their work by transmitting the useful light (about 85% of it, on the average) and reflecting most of the hot, useless infrared rays back into the lamphouse. Interference filters do not themselves get as hot as absorption-type filters, and accordingly do not require such energetic refrigeration to prevent their destruction. Nevertheless, the microscopically thin layers with which they are coated gradually deteriorate in the reflected arc beam, and may burn off quite suddenly, with cracking of the glass, if the beam is accidentally concentrated to a focus upon them.
Another method of reducing the temperature of the directly irradiated film is the use of an air-jet at the projector aperture. This method does
not prevent heat from being generated in the film by absorbed radiation, but it does help to remove it before the temperature rises high enough to scorch the emulsion. Because it is likely to aggravate the fluttery in-andout-of-focus movements of the film, air-cooling is not generally desirable except in the few unusual cases where it must be used as a last resort.
Big Arcs Require TufCold Mirrors
The Strong TufCold interferencetype reflector has made the use of heat filters and air-cooled film gates unnecessary even when such powerful modern lamps as the Strong Mighty-90, Super-135, U-H-I, and 35/70 Special, among others, are employed for the realistic, daylight-bright widescreen projection increasingly demanded by the moviegoing public.
On the whole, projection engineers feel that simplified high-intensity ("Suprex") lamps fitted with ordinary silvered mirrors do not require the use of heat filters when operated at arc
currents below 75 or 80 amperes. The radiant-energy flux at the center of the 35mm film aperture ranges from 0.7 to 0.8 of a watt per square millimeter at these currents with this type of arc lamp. On the other hand, some method of reducing heat must be used with all rotating-positive high-intensity lamps, inasmuch as these lamps have large mirrors (16", 16i/2", and 18") and burn from 75 to 180 amps. (0.8 to 1.2 W/mm2).
The effect of the Strong TufCold reflector in reducing aperture heat — the heat on the film due to direct irradiation — is almost magical! Even though delivering substantially more light to the screen than a silvered mirror used in conjunction with a heat filter, the TufCold reduces heat at the center of the aperture to 0.4 or 0.5 W/mm2 with rotating-postive reflector lamps at high arc currents, and results in a center-aperture flux of only 0.6 to 0.7 with the most powerful projection lamps in existence, the Strong Jetarc and the National Ventarc, each
International Projectionist
April 1961