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exposure periods, there is marked improvement in screen image definition.
Experiments so far have been directed toward the use of the modulated front jet. It is quite possible to use the opposite arrangement of a steady front jet and pulsed rear jet. For better cooling, however, it seems advisable to let the continuous air stream wash the emulsion side of the film, relying on the front jet as the position correcting agent. A pulsed combination of both jets may offer some advantages in air economy, but has not been tried.
References
1. E. K. Carver, R. H. Talbot and H. A. Loomis, "Effects of high-intensity arcs upon 35mm film projection," Jour. SMPE, 41: 69-87, July 1943.
2. E. K. Carver, R. H. Talbot and H. A. Loomis, "Film distortions and their effect upon projection quality," Jour. SMPE, 47: 88-93, July 1943.
3. F. J. Kolb, Jr., "Air cooling of motion picture film for high screen illumination," Jour. SMPE, 53: 635-664, Dec. 1949.
Discussion
R. T. Van Niman (RCA Victor Div.) : I perhaps missed something in the early part
of the talk, but did you consider whether or not the amount of deformation varies with the type of picture material? I believe Mr. Kolb pointed out that the amount of buckling depends to some extent upon the density of the film in the aperture at that time.
Mr. Borberg: Yes, it does matter, but there is always deformation, even with a very low density. The worst condition occurs with a dark film, and necessarily the amount of buckle depends also on the energy of the light source.
Mr. Van Niman: No attempt has been made to compensate for the variation in density along the film then?
Mr. Borberg: No. A photocell device operating from screen illumination to control air blast has been considered. Such a device would compensate for scene-to-scene variations which are beyond the projectionists' ability to follow, but the instrumentation just hasn't gone that far.
W. W. Lazier (National Carbon Co.}: Does the intermittent air blast make much audible noise?
Mr. Borberg: Yes, there is some noise, but it's not very disturbing and it does not exceed the noise of jets with continuous air. There is a purring noise, I might say.
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August 1952 Journal of the SMPTE Vol. 59