| 摘要 |
<p>A focus detecting mechanism wherein the light reflected on an object surface (25) is diffracted by a hologram element (23). The diffracted light includes two astigmatic convergent beams which form least circles of confusion on long photodetector means (29) and (30) in the same plane close to a focal plane (22f) of a lens (22), and a focus signal is obtained on the basis of a differential output from these photodetecting means. Since two diffracted beams having least circles of confusion on the same plane, the photodetecting means can be placed horizontally, and a focus detecting mechanism can be made easily with an improved dimensional accuracy. In spite of the use of a hologram element, the fluctuation of wavelength can be absorbed, and the reliability of the device is very high.</p> |
