| 摘要 |
PURPOSE:To reduce spherical aberration and astigmatism as much as possible and to find a focus position by using a concave mirror which has two split reflecting surfaces whose centers of curvature are eccentric slightly in the direction of the splitting line as a split optical element, forming at least one aspherical surface of a condenser lens which forms an image of an exit pupil on the split optical element, and splitting an image of an object to be photographed into two and detecting the coincidence between both images. CONSTITUTION:The concave mirror 21 is divided into two left and right areas 21A and 21B and the centers 32A and 32B of curvature of those areas 21A and 21B are shifted slightly in the direction of the splitting line 31 to constitute a focus position detector. Light passed through a slit 41 is reflected by a mirror 42 to make incident to an aspherical condenser lens 12 and the transmitted light is reflected by the split concave mirror 21 and simultaneously split into two pieces of luminous flux and condensed to make incident to the aspherical condenser lens 12 again. The light projected from the aspherical condenser lens 12 is passed between the upper and lower spaces of the mirror 42 to make incident to two sensor arrays 14. |
