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TO NEC CONTACTOR
Fig. 6. Schematic circuit of power supply for servoamplifiers.
cycle output are adjusted for minimum residual signal at the output of the amplifiers when the photocells are dark and the outputs of the reference voltage potentiometers are grounded. The germanium and selenium diodes across the relay coils are for contact spark suppression.
The filters associated with the photocells have been chosen so that the spectral sensitivity of the photocell as modified by the filter matches approximately the spectral sensitivity of the respective component of the color print emulsion. For measuring the red exposure, an SI photosurface and a Kodak Wratten Filter No. 29 are used; for the green, an S4 photosurface and Kodak Wratten Filters Nos. 57A and 16 are used; and for the blue, an S4 photosurface and Kodak Wratten Filters Nos. 47 and 2B are used.
The same relatively sharp-cutting filter combinations are used to filter the three beams in the optical system in order to provide a wide range of control of color balance. If less selective filters were used, a given filter might permit enough leakage of light in an adjacent band so that the exposure
in that band could not, in extreme cases, be reduced to a sufficiently low value. This would only occur when printing badly unbalanced negatives. If experience proves that negatives are relatively uniform in color balance, less selective filters can be substituted in the optical system, with a resulting increase in the available overall exposure.
Performance
The normal operating speed of this printer is 100 fpm. The lamp used is a 1000-w, 120-v, T-12 prefocus lamp, operating at 100 v. Under these conditions there is a 0.6 log E margin in exposure above that required from printing a normal negative onto Eastman Color Print Safety Film, Type 5381. As first stated, the tape-controlled exposure adjustment covers 0.62 log E in 0.02 log E steps, or a total of 32 steps. If the system is adjusted so that a normal negative prints at Step 16, then there is a range of ±0.30 log E available for overand underexposed negatives.
The lamphouse is cooled with a 200cfm blower and the air path through the lamphouse and light baffles is designed for a minimum of resistance so that the
J. G. Streiffert: Control for Color Printing
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