| 摘要 |
A light valve of a film printer has vanes set by the expansion of a plurality of slides parallel to a first axis. The slides are individually actuatable parallel to a second axis transverse to the first axis in a path between a first position and a second position so that the slides expand parallel to the first axis an amount depending upon the combination of slides actuated into the second position and are movable as a unit parallel to the first axis responsive to a trim adjusting knob. A carriage mounted on the light valve is movable parallel to the first axis. A sensor individual to each slide, preferably a light source and a light detector, intersects the path of such slide to indicate whether it is in the first or second position. The carriage is coupled to the trim adjusting knob so the carriage moves parallel to the first axis as the slides are moved as a unit responsive to the trim adjusting knob, to maintain the slides between the respective sensors. Preferably, the sensors and a slide register that actuates the respective slides are coupled to a comparator to stop film transport when the indications of the sensors and the contents of the slide register do not match.
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