| 摘要 |
PURPOSE:To drive a lens to the focus position at a time by measuring the size of the image of reflected light at three points to obtain the absolute value of an extent of deviation. CONSTITUTION:A CCD camera 14 is placed in a position conjugate to the image of a target. A CCD camera 15 is placed before the CCD camera 14 with respect to image. A CCD camera 16 is placed after the CCD camera 14 with respect to image. A diameter detector 7 obtains the size (diameter) in accordance with images obtained by CCD cameras 14, 15, and 16. A focus detector 8 obtains the present focus position in accordance with the beam diameter obtained in this manner. A driving device 9 drives a condenser lens. That is, since a true focus position is in the middle between CCD cameras 14 and 15, the difference between the present focus position and the true focus position is used as an extent of driving to drive the lens. |
