| 摘要 |
PURPOSE:To improve the operativity of free surface error measurement by guiding light from a convergent illumination system so that the light is converged to a specific diameter at a regular position, and guiding its reflected light to a detection position. CONSTITUTION:When a measured point is at a measured position on a regular plane, laser light from a prism 4 and laser light from a half-mirror 5 are guided to the measured position, and their light spots are superposed on each other at the measured position on the regular plane. For the purpose, the prism 4 is turned over and the reflected light from the light spot on the regular plane is guided to a detecting light shield plate 6 through the prism 4, so that the reflected light from the light spot of the laser light from the half-mirror 3 is guided to the aperture of the light shield plate 6. A detector 7 for the quantity of photodetection detects the quantity of the reflected light and outputs its detection signal to a decision circuit 9. Then, the circuit 9 compares the regular quantity of photodetection with the quantity of photodetection based upon the detection signal to judge whether the measured position is on the regular or not. Then, the circuit 9 outputs an output signal corresponding to the measured position. |
