| 摘要 |
PURPOSE:To increase detection sensitivity for displacement without changing optical systems, by increasing the image displacement detection sensitivity of a photoelectric detector by allowing gradient sensitivity areas of two photodiodes to overlap with each other. CONSTITUTION:A photoelectric detector for focusing a light beam is constituted including photodiodes, and has an area wherein photodetection sensitivity is constant and a gradient sensitivity area which is close to the constant sensitivity area and wherein photodetection sensitivity decreases gradually toward the constant sensitivity area. Among said photodiodes, at least two specific photodiodes are arranged adjacently in such a way that the gradient sensitivity areas overlap with each other at a prescribed boudary part. Further, a light spot is formed at the prescribed boundary part so that >=20% of a light forcused image is incident to the gradient sensitivity area, and the displacement of the light focused image is detected by a difference in output between said two specific diodes. |
