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April 1935
INTERNATIONAL PROJECTIONIST
21
ARC DATA SUMMARY
(Continued from page 19) observations anent comparative quality.
He first admits that the D. C. Suprex is very good, so good in fact that he draws a direct comparison between this type arc and even the high-intensity arc at 125 amperes. So far so good.
He repeats his analogy between an incandescent lamp and an arc used for motion picture projection, which employs a shutter. Shutter flicker, continues Mr. Hoffman, we shall always have with us. In this he is quite correct. So very correct, in fact, that he bears out our contention that flicker, tolerable in a lowintensity lamp, is wholly unacceptable in a high-intensity A. C. arc.
Accepting the statement that the D. C. Suprex arc at 45 amperes gives 50 per
cent more light than does the A. C. arc at 80 amperes, Mr. Hoffman seizes upon this fact to drive home the thought that this is precisely the reason why the D. C. arc gives more flicker than does the A. C. This statement is unacceptable in the light of established projection practice and in the absence of any data tending to sustain such a theory.
Possibly Mr. Hoffman is confusing travel-ghost with "shutter flicker," which, as far as we know, occurs with D. C. operation only when there is excess illumination; and if the latter were true, certainly the field would not have searched long for, and now be eagerly turning to, Suprex arcs.
Reconciling Frequency Difference
The one assertion made by Mr. Hoffman that neither this writer nor any
others with whom he has discussed the matter are able to understand — and, let it be said, the most important point under consideration herein — is the procedure followed in reconciling the difference in frequency between the 60-cycle A. C. and that of (48) of the shutter. This is, or should be, the focal point of Mr. Hoffman's presentation.
Oscillograph curves to the contrary, this is the one question that must be answered in detail before anybody will give serious consideration to the A. C. arc. Word has filtered through from various sources that there exists a rational answer to this question, but this publication has never been honored with the details thereof.
This writer is positively not suffering from any rectifier complex, as Mr. Hoffman asserts. Motor generator manu
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