| 摘要 |
PURPOSE:To accurately detect an in-focus and an out-of-focus state of a low- contrast object by improving an S/N ratio by correcting an analog reference voltage and the operation characteristics of photodetecting elements. CONSTITUTION:Output voltage from respective photodetecting elements in photodetecting element arrays 18A and 18B are applied simultaneously to sample holding circuits 26A-1-26A-n, and 26B-1-26B-n, and the hold voltage of each circuit 26A is applied to comparators 29-1-29-n. Each comparator is applied with a stepwise analog reference voltage from a D/A converter 32 in parallel and during the inversion of comparison outputs, write signals are supplied to digital memories 33-1-33-n. Each memory 33 is supplied with a digital signal, which has prescribed relation with the reference voltage, from a processing circuit 31 in parallel and stored when the write signals are supplied. Then, the reference voltage is varies within a prescribed range to store the outputs of the photodetecting elements, thus accurately detecting the focusing state of an object moving at a high speed. |
