| 摘要 |
PURPOSE:To provide an optical system of simple construction by making use of the fact that the image on a diffraction grating goes sharp when focus is matched and forms an image having color blurrs when it is not matched, electrically detecting this and performing detection of the focus. CONSTITUTION:The light from an objective lens 1 is split to optical paths L1, and L2 by a beam splitter 2, and the image by the L1 is formed on a diffraction grating 3. A photodetector 4 consisting of two adjacent photoelectric elements 4A, 4B is disposed on the rear surface of said grating. A photodetector 5 of the same construction as the 1st photodetector 4 is disposed in an optically conjugate position. The difference in the outputs of the elements 4A, 4B and the difference in the outputs of the 5A, 5B are detected, and further the difference in these two outputs is detected. Hence, focusing is accomplished in such a way as to eliminate the blurring of color at the boundary of the bright part and dark part of the image on the element 4, whereby the focus detection of a camera or the like is accomplished with the extremely simple construction. |
