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1050 Transactions of S.M.P.E., Vol. XII, No. 36, 1928
i ■ 6(logF-logK)+logF-loga
(3) logi=
bM
as a function of voltage.
Intensity Requirements for Printing with Duplicating Film
The foregoing discussion and the data concern printing on regular positive film. An attempt was made to obtain similar data for duplicating film. This problem is complicated by the rather indefinite requirements of duplicating film printing, and by the failure of the reciprocity law with duplicating emulsion which renders the data of doubtful application at other than the specified intensity level.
The quality requirements for a duplicate negative or a master positive differ widely from those of a projection print. Moreover the tolerance in the limits of exposure is greater. To make a duplicating film print of quality similar to that of a good positive projection print requires from four to five times the intensity. To make a satisfactory master positive, perhaps from 10 to 30 times the intensity should be used. When filters are interposed between lamp and aperture to regulate contrast, the intensity required because of absorption is about 2.5 times that of the unfiltered light. This factor holds with fair accuracy for either one layer of Aero No. 1 or for two layers of No. 39, or equivalent glass filter, which are the filters generally used for duplicating film.
A printer which will make satisfactory master positives on duplicating film for the large range of negative densities probably should have an exposure range from 10 m.c.s. for the thinnest negative printed without filter to about 2500 m.c.s. for the most opaque negative printed with a filter. The extremes of this range will of course seldom be used in practice but a lamp which will accommodate the extremes might be advisable.
Variation of Photographic Intensity with Wattage for Duplicating Film
It was found by repeating on duplicating film the work which was done with positive film that the wattage-intensity relation already quoted for positive film holds with sufficient practical accuracy in the case of duplicating film for measurements made