| 摘要 |
A method and apparatus for establishing optimum film exposure time for documents of different reflectances, A photo-sensor is used to produce a signal proportional to the intensity of light reflected from the document to be microfilmed, The signal is integrated and a time is determined for the integrated signal to reach a threshold or reference value, The time needed to reach the threshold value is measured very accurately by a microprocessor, The measured time is then convened to new time by using a look-up table, The new or desired shutter time is controlled by the microprocessor by terminating the exposure when the total time the shutter was open equals new exposure time found in this look-up table.
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