| 摘要 |
PURPOSE:To put a focus on only the surface of a transparent body by moving a movable mirror toward the side opposite to the transparent body in parallel and increasing the angle of irradiation of measurement luminous flux, and reflecting measurement luminous flux which is reflected except by the surface of a transparent body in such a direction that it is not incident on an objective. CONSTITUTION:The movable mirror 6 is moved toward the side A opposite to the transparent body in parallel to refract measurement luminous flux (c) which is reflected by a fixed mirror 7 on the outer peripheral part side of the objective 8, thereby projecting measurement luminous flux (d) on the transparent body 4 at a large angle theta1 of irradiation. Then pieces of measurement luminous flux (e) and (k) reflected by the top surface 4a and reverse surface 4b are both large in angle of reflection, and the measurement luminous flux (k) reflected by the reverse surface 4b is reflected in such a direction that it is not incident on the objective 8. Only the measurement luminous flux (e) reflected by the surface 4a is refracted by the objective 8 and a focus positioning mechanism is operated with the measurement luminous flux (e). Consequently, even the transparent body which is hardly sensed optically can be put in focus accurately and instantaneously. |
