| 摘要 |
PURPOSE:To suppress the loop gain in a circuit and to simplify constitution by detecting the output level of the other photedetector when the output of one photodetector attains a prescribed level at every specified light emission cycle. CONSTITUTION:IR light of the quantity larger than on the photodetector 12A is made incident on 12B when a subject is near and a photographing lens is focused to a remote point. Then the output 5 of an integrator 19B attains a refence level Vs earlier than the output 5' of 19A and the output 6 of a comparator 20B rises to an H. An output signal 7 via an OR circuit 21 turns off switches 18A-18C to stop the light emission from the light emitting element 11. The integrators 19A, 19B are simultaneously changed over to a constant current source 23 and the output 5' attains the level Vs as well. A signal 9 to move the photographing lines in the near distance direction is outputted to a motor driving circuit 24 from a logical circuit 22 during the time when the output 6 rises to the H and the output 6' of the comparator 20A rises to the H. The need for obtaining the ratio of the two detection signals is thus eliminated and the loop gain over the entire part of the circuit is decreased, by which the circuit constitution is simplified. |
