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cooling of the lamp, lamphouse, and condenser system is very effective. Also, as mentioned, the lamp can be undervoltaged by 17% with adequate margin of exposure. Under these conditions it is estimated that the lamp life should be of the order of 200 hr. In a system of this type with servocontrol of exposure, there need be no concern regarding blackening of the lamp or fluctuations in line voltage. These factors affect only the maximum available exposure. Below this maximum, the exposure is substantially independent of the lamp voltage or its condition.
The response time of the servosystem is about 0.02 sec. Thus, at a printing speed of 100 fpm, the exposure change is effected in one-half the frame height.
Because of the large vertical angle between the three light beams, color
fringing will occur if there is poor contact between the films. Thus, the divergence between the colored beams is, in a sense, an advantage in that it gives a positive indication of poor printer performance.
Discussion
Paul Ireland (EDL Company}: Is there any provision for the calibration of this to take care of drift in the photocell?
Mr. Streiffert: Not inherently in this system. I have a photoelectric exposuremeasuring device which consists of a bracket which I can screw in front of the printing aperture and in which I can insert photocells with appropriate filters — the same filters which are used in the optical system. That's connected to a vacuum tube voltmeter and is used for checking exposure from time to time to be sure that it's constant.
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November 1952 Journal of the SMPTE Vol. 59