| 摘要 |
PURPOSE:To perform focusing operation by irradiating an object with light beam flux while the optical axis is aligned with the axis of an objective, passing its reflected light through a cylindrical lens and photodetecting the light, and detecting defocusing from the shape of its spot and varying the distance between the object and objective according to the defocusing quantity. CONSTITUTION:The object W is irradiated with the light beam flux from a light source 9 after the light beam flux passes the axis of the objective 5, and its reflected light beam flux is transmitted through the objective 5 and cylindrical lens 15 and made incident on a CCD camera 17. The spot shape of the luminous flux is discriminated to detect the defocusing and a stepping motor 19 is driven according to the detection result to vary the distance between the surface of a work W and the objective, thereby focusing the light flux. Consequently, the focusing position can be made constant regardless of the focusing operation and an optical system can easily be assembled in a short time. |
