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646 KOLB December
Under projection conditions approximating that of a first-run de luxe house, we have observed film motion of approximately 0.020 to 0.025 inch from the flat plane as a reference. With intensities in excess of what film will stand for repeated projection, we have observed a maximum negative drift of approximately 0.045 inch.
(2) Embossing
At higher levels of projection intensity (and the first-run de luxe houses have now reached this value), embossing of the film is observed. This is a permanent film deformation, resembling an incomplete recovery from the negative drift just discussed. Actually, two types of embossing are observed: (a) frame embossing, wherein the entire area of each frame appears to be raised slightly above the normal surface of the film — as a row of separate pincushions — and (b) image embossing, wherein the dark and light areas of the image are seen by reflected light to be at slightly different elevations from the nominal film surface. These two types of embossing probably begin simultaneously somewhere in the range of mean net radiation intensity 0.20 to 0.30 watt per square millimeter. Of course, at the lower intensities the embossing is minute, and can be observed only with difficulty when the film is examined under low-angle reflected light. With increasing intensities, the amount of embossing increases until it can be seen when the film is examined under normal illumination. Even when the film is severely embossed so that the center of each frame is displaced as much as 0.005 to 0.010 inch from the film plane, we have never observed any deterioration of image quality or any visible indication on the screen that this film is different from unembossed film.
(3) Change in Reflected Image Tone
Some types of film, after projection at higher intensities, show n change in reflected image tone even though the image tone by transmission is not affected. This phenomenon appears somewhere in the region of 0.30 mean net watt per square millimeter. Film thus affected shows a warmer tone when the film itself is examined by reflected light, and the tone, of the frame is seen to be different from the original tone of the unprojected frame lines and film edges. No satisfactory explanation has been offered for this phenomenon; it is one of those occurrences which, though interesting, have no influence on the quality of the projected image.