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June, 1941]
MEASUREMENT OF PRINTING DENSITY
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is not a constant but a function of density value, no single printer factor will cover the operating negative density range. The chances for error in this procedure are too well known to require further comment here. With the substitution of printing density control only one calibration for each type of printer is necessary, no matter how many different types of negatives are employed.
Conclusions. — It has been shown that when the integrating sphere type of densitometer is equipped with a combined cell and filter that gives an overall spectral response similar to that of positive film, photographic printing densities may be measured of either sound or
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LOG RELATIVE EXPOSURE
FIG. 10. Illustrating printing and visual H&D curves for Dupont 222 sound negative.
picture negatives varying widely in grain size and color of base. It has also been shown that the printing density is relatively independent of the type of light-source or light-filter employed in the printer.
The addition of this alternative type of filtering to the integrating sphere densitometer makes it possible to eliminate all color coefficients and other devices currently employed in the "timing" of various types of negatives. The use of such an instrument, therefore, should clear up the confusion which exists at present in laboratories employing diverse types of negatives and should increase considerably the efficiency of the film processing operations.