| 摘要 |
PURPOSE:To stop driving a lens once potentials at input terminals of a comparator become coincident with each other when the output of one photodetecting circuit attains to some set value, by varying the light emission frequency of a light emitting element to the center frequency of a band-pass filter circuit. CONSTITUTION:Output processing circuits of photodetecting elements 23 and 24 incorporate BPFs 27 and 28. The light emission frequency of the light emitting element 22 is varied to the center frequency of the BPFs within a specific time. When the output Vj of one photodetecting element circuit attains to some set value, the output state of the other photodetecting element circuit is stored as a voltage value and supplied to the inverted input terminal of the comparator 43. While the photographic lens is driven from its limit value to the other limit value, the potential (+) at the other input terminal of the comparator circuit is swept from the limit value to the limit value, and the photographic lens is stopped from being driven when the potentials at both input terminal coincide with each other. Thus, the distance measurement state is discriminated stably through such constitution that the light emission frequency of the light emitting element is varied to set the photographic lens at the specific position. |
