| 摘要 |
PURPOSE:To detect stably an out-of-focus quantity by spreading a light out of a light sensing region on a detector very much to reduce sufficiently the sum of a detection signal if the out-of-focus quantity is very large. CONSTITUTION:The value of an optical parameter is so determined that the sum of the quantity of laser light irradiated onto light detecting cells 16-1 and 16-2 on a photodetector 16 is small when the outer-of-focus quantity is very large. That is, the output voltage of an adding circuit 25 is reduced when the out-of- focus quantity is very large; and therefore, a certain reference value is determined in a CPU27, and it is judged that the out-of-focus quantity is very large if the output voltage of the adding circuit 25 is lower than this value. When the out-of-focus quantity is very large, the laser spot on the photodetector 16 is spread out of light detecting cells 16-1 and 16-2 very much for the purpose of reducing the sum of the quantity of laser light irradiated onto light detecting cells 16-1 and 16-2. |
