| 摘要 |
PURPOSE:To position a focus on an opaque body itself even when the opaque body is put in focus with a transparent body between by moving a movable mirror toward the opaque body in parallel and decreasing the angle of irradiation of measurement luminous flux. CONSTITUTION:The movable mirror 6 is moved toward an object B in parallel to projects measurement luminous flux (d) at a small angle theta1 of irradiation closely to an optical axis 5. The measurement luminous flux (d) is projected while close to the optical axis 5, the measurement luminous flux (d) impinges on the opaque body 20 unless the opaque body 20 is extremely small. When the measurement luminous flux (d) impinges on the opaque body 20 once, measurement luminous flux (i) reflected by the opaque body 20 is intenser than measurement luminous flux (e) reflected by the surface 19a of the transparent body 19, so a focus positioning mechanism is operated with the reflected luminous flux (i) to put the focus on the surface of the opaque body 20. Consequently, even when the transparent body which is hardly sensed optically is interposed, accurate, instantaneous focus positioning operation is enabled. |
