| 摘要 |
PURPOSE:To accurately detect the focus position with a miniature and simple device from the output difference of a pair of photo detectors having optical serrations disposed near the best image plane of a concave lens by passing the incident light from a photographic lens through the concave lens thereby forming the impage in which the minimum circles of confusion spread. CONSTITUTION:Light from an object 10 is imaged on a photo detector 13 through a photographic lens 11 and a concave lens 12 having negative power. The minimum circle of confusion 15 on the photo detector 13 is made larger than the minimum circle of confusion 16 of the case when no concave lens 12 is provided by the concave lens 12. The photo detector 13 consisting of a pair of photo detectors 13a, 13b is provided in this position and the image is formed thereon, whereby the minimum circle of confusion 15 may be obtained and always the same image may be formed on a pair of the photo detectors 13a, 13b. Further a pair of photo detectors 13a, 13b given optical serrations in front of either one of said elements are used and the focus position of the photographic lens is detected based on the output differences of a pair of the photo detectors 13a, 13b. |
