| 摘要 |
PURPOSE:To control a driving system for automatic focus detection by detecting synchronously outputs of two photodetector areas with a signal which does not synchronize with a pulse-modulated signal, and detecting only external light components inputted to the two photodetector areas on the basis of the synchronous detection outputs. CONSTITUTION:Pulse-modulated projection spot light is projected by a projecting element 31 on an object and its reflected light is photodetected by the two areas 35A and 35B, whose outputs are detected synchronously by the 2nd synchronous detecting circuits 61a and 61b with a signal which does not synchronize with the pulse-modulated signal, i.e. asynchronously with the 1st synchronous detecting circuits 42a and 42b. Only external light components are extracted as their output signals and inputted to a comparator 64 to calculate their difference, which is inputted to a succeeding stage comparator 65 to judge whether the difference is larger than a constant level VC or not; when the difference is larger than VC, it is inputted to a control circuit 51 to control the driving of a motor 36 for driving an image formation optical system. Consequently, stable operation is performed even against an object with large contrast. |
