| 摘要 |
PURPOSE:To improve virtual sensitivity for a dark object and to prevent an excessive deterioration of SN ratio by so making the AGC as providing a constant optical information level of the solid-state image pick-up element based on the illuminance information. CONSTITUTION:The light from an object that passed through a lens 20 and a diaphragm 21 reflects at the film surface of a shutter 22, and is converted to a photocurrent by a silicon photodiode 37 in proportion to its illuminance level. The photocurrent is lead to a photometric circuit 38 composed for instance of logarithmic amplifier, and converted to a voltage, and its output is added to a threshold value setting circuit 39. The output from the circuit 39 is sliced in its high level part, and supplied to the current source of the differential amplifier of an AGC circuit 30 as a control output converted by exponential convertion. Accordingly the output of the circuit 30 becomes constant regardless of the illuminance variation of the object. The optical signal from a CCD image pickup element thus obtained as above described, is subjectected to a prescribed processing by a signal processing circuit 31 and supplied to a magnetic head 34, and recorded in a magnetic disc 35 through a recording amplifier 32 and a changeover switch 33.
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