| 摘要 |
PURPOSE:To considerably expand the detection range of focus errors by providing a wave front converting means such as slit in the optical path of reflected light from a light focusing target face. CONSTITUTION:The parallel beams from a light source are reflected by a mirror 12 and are projected to a light focusing target face 7 via an objective lens 3. The reflected light passes again through the lens 3 and is made into parallel beams which arrive at the mirror 12. Since a slit 12 which is a wave front converting means is provided to the mirror 12 in a position off from the optical axis, part of the reflected light passes the slit 13 and is applied via focusing lens 5 to a bisected light detector 14. A focus error is detected by the difference in the quantities of light received in the right and left photodetectors forming the detector 14. Since the device is formed in this way, an unbalance in the quantities of the light received in the right and left photodetectors occurs even when the target face 7 is in a position extremely deviated from the focal position, whereby the detection range is expanded. |
