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644 KOLB December
For normal projection where the initial film temperature may be 80 degrees Fahrenheit, this represents a maximum emulsion surface temperature of 320 degrees Fahrenheit and a maximum base temperature of 300 degrees Fahrenheit.
We have no conclusive experimental method of determining how nearly correct these temperatures may be, but what evidence there is suggests they are not greatly in error. It is probable that film is able to perform as successfully as it does only because these peak temperatures are maintained for such short periods of time (as shown by the rapid equalization in Fig. 4), since film held continuously at these temperature levels distorts and loses essential physical qualities very rapidly.
HIGH-INTENSITY EFFECTS
When film is projected at these higher intensities, a series of phenomena occur, depending upon the particular projection intensity being studied. Many of these effects have been described by Carver, Talbot, and Loomis1 and hence only a brief review is needed here. Listed in order of their appearance with increase in radiation intensity, these effects are summarized in Table I.
TABLE I HIGH-INTENSITY PHOJECTION OF FILM
Intensity Threshold
Projection Phenomenon
Mean Net Watts/Mm2
L 2. 3,
4. 5. 6.
7.
Negative drift Embossing Change in reflected image tone Focus drift Image flutter In-and-out of focus Blistering
0.20-0.30 0.30 0.35-0.40 0.40 0.50 0.60-0.65
Of these phenomena, negative drift is an entirely normal film characteristic which is present to greater or lesser extent in all cine projection. Embossing and 'the change in reflected tone have never, in our experience, contributed any deleterious effect to screen quality. Focus drift is perhaps a necessary evil that must be tolerated if maximum projection intensities are to be used. Image flutter is