| 摘要 |
The originals to be photographed are transported past a measuring station and an aperture at a filming station. The microfilm is transported past a film aperture at the filming station. The originals vary in length (measured in the direction of transport) from a maximum to a minimum length. The measuring station is spaced a distance from the filming station which corresponds to the maximum length. Each original is scanned in a direction perpendicular to the direction of transport at the measuring station and the peak amount of light reflected from the original is stored. The number of storage units is equal to the number of originals of smallest length which can be accommodated in the distance between the filming and measuring stations. For each storage unit, a monostable multivibrator is furnished which is started when the corresponding original leaves the measuring station and whose time constant is such that its trailing edge occurs just prior to the time the same original reaches the filming station. A step switch controlled by the trailing edges of the multivibrators connects the output of each storage unit in turn to the input of a differential amplifier whose output in turn controls the position of a filter or diaphragm controlling the light falling on the original at the filming station.
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