| 摘要 |
PURPOSE:To adjust a focal point in a simple manner by providing a detecting means which casts the light reflected from an object to dividing photodetectors and detects the shift of the focal point in accordance with the output of each detector, and a changing means for changing the distance between the object and an objective lens. CONSTITUTION:A laser light is cast to the surface of a work W through the axial center of an objective lens 5. This apparatus adjusts a focal point from the light reflected from the surface of the work W according to the astigmatism method. Therefore, a spot on the surface of the work W is set at the same position at all times, and a focal point can be adjusted at a desired position on the surface of the work W in a simple manner. When the reflecting light is cast to each four-dividing photodetector 29, 33 by changing the refracting direction in a longitudinal and a lateral directions, the influences of the roughness of the surface of the work can be removed through a predetermined operation. Moreover, since the position of a CCD camera 7 is set for every kind of the lens 5, the shift of the focal point at the detecting side from that at the camera side because of the influences of the chromatic aberration can be corrected. Accordingly, the focal point can be always met correctly irrespective of the kind of the lens 5. |
