| 摘要 |
PROBLEM TO BE SOLVED: To detect beam vignetting by simple constitution and to prevent the large defocusing of an object at the closest distance by judging that the object is at the closest range or at infinity according to the outputs of two light receiving means. SOLUTION: When the output of a PSD 32 of a distance detecting circuit 30 is lower than a prescribed level and the output of a PSD 42 of a beam vignetting detecting circuit 40 is higher than the prescribed level, it is judged that an object is located at a closest distance and a light beam is out of the light receiving surface of the PSD 32, so a photographic lens is immediately driven to the closest range. When the output of PSD 32 is higher than the prescribed level and the output of PSD 42 is lower than the prescribed level, the object is located at a close distance and since detection of beam vignetting is disabled, LED 80 is put on and warning is issued to a photographer. Finally, when both outputs of the PSDs 32, 42 are lower than the prescribed level, the object is located at a long distance, it is judged that the reflected light beam is feeble and the photographic lens is driven to the position at infinity. |
