| 摘要 |
PURPOSE:To electrically detect focus by the simple constitution wherein a photodetector consisting of at least two pieces of photoelectric elements adjoining by way of a boundary line extending in the direction intersecting with the refraction direction of a refractive optical element is provided on the rear surface of the refractive optical element in close contact therewith. CONSTITUTION:An objective lens 51 forms images on a diffraction grating 52, and a photodetector 53 consisting of two adjacent photoelectric elements 53a, 53b is provided on the rear surface of this grating 52 in close contact therewith. The outputs of the elements 53a, 53b are inputted to a detecting circuit 54, which detects the difference in the rates of change in the outputs of both elements with the movements of focus. The output of the circuit 54 is inputted to a servomotor 57 driving a pinion 56a meshed with a rack 55a provided to an arm 55 holding the lens 51, and when the difference in said rates of change goes to zero, the servomotor 57 is stopped, thereby stopping the objective lens 51. |
