| 摘要 |
PURPOSE:To perform error-free detection by converting an image formed in the 1st stop-down state and an image formed in the 2nd stop-down state different from the 1st stop-down state photo-electrically by a photodetecting element arranged on an expected image-forming surface , and comparing those images with each other. CONSTITUTION:Image contrast varies with lens extension as shown by a curve A at open aperture or as shown by B in a stop-down state. For this purpose, an increase in difference in contrast is utilized in an out-of-focus state to detect focusing. The stop 4 of the lens 1 is driven to small aperture 4a during light measurement, and an open-aperture and a small -aperture image are converted photoelectrically by the photodetecting element 5 such as the CCD; and contrast values A and B are calculated, thereby judging a focusing state when B-A is smaller than a constant or an out-of-focus state when not. Luminous flux from an objective may be split and photodetected through image forming systems which differ in aperture. |
