| 摘要 |
PURPOSE:To set a lens at a specific position by varying the characteristics of a filter and increasing the output of a photodetecting element circuit from zero or a fine value, and deciding on a distance measurement state. CONSTITUTION:The outputs of photodetecting elements 6 and 7 are sent out through BPFs 10 and 12 having variable characteristics, and an FF36 is held at a level H when the voltage Vf at a point (f) reaches a reference voltage Vr. At the same time, the output of an INV30 is held at a level L and a capacitor 31 is charged up to the voltage V1. This voltage V1 is amplified by a buffer circuit 32 and supplied to the inverted input terminal of a comparator (CMP)33. An AND gate 37 is therefore opened and a transistor (TR) 38 is turned on to energize an electromagnet 39. When the potential at the uninverted input terminal (+) of the CMP33 drops to the potential at the inverted input terminal (-), its output goes down to the level L. Consequently, the AND gate 37 is closed to fix the photographic lens at the specific position. Thus, the photographic lens is set at the specific position through stable operation. |
