| 摘要 |
PURPOSE:To improve the distance measuring precision even for a close-distance and low-reflectivity object by extending the integral action time if distance measurement is impossible because the reflected light is in a low level in an active automatic focusing device. CONSTITUTION:Outputs of two areas A and B to which a photodetector 6 is divided are amplified by amplifiers 8 and 9 and are detected by detectors 10 and 11 and are integrated by integrators 12 and 13 to obtain outputs VA and VB, and VA+VB and ¦VA-VB¦ are obtained by an adder 14 and a differential device 15 and are compared with levels VL and VD by a comparing circuit 16. The in-focus state, the front focus, or the rear focus is discriminated on a basis of comparison results by a microcomputer 17, and a motor 19 is driven by a motor driving circuit 18 to move a lens group 1, a light projecting element 2, and a photodetector 6, thus focusing. If the microcomputer 17 discriminates that distance measuring is impossible because of a lack of the reflected light, an integral action time setting circuit 20 sends a signal, which extends the integral action time to its maximum, to integrators 12 and 13. |
