FOCUS SERVO DEVICE, SURFACE SHAPE MEASURING INSTRUMENT, COMPOUND MEASURING INSTRUMENT, FOCUS SERVO CONTROL METHOD, FOCUS SERVO CONTROL PROGRAM, AND RECORDING MEDIUM WITH THE PROGRAM RECORDED THEREON

摘要

PROBLEM TO BE SOLVED: To provide a focus servo device which performs accurate focusing even in the case that there is disturbance light.;SOLUTION: An objective lens is controlled to a focus position on the basis of focus signals S_F. A signal processing part 230 outputs the focus signal S_F and a received light quantity signal S_AB. In a light quantity level comparison part 410, the received light quantity signal S_AB is compared with a light quantity level threshold 421. When the received light quantity signal S_AB is below the light quantity level threshold 421, a control operation is stopped. In a signal level comparison part 450, the level of the focus signal S_F is compared with a focus signal level threshold 451. In the case that the focus signal S_F exceeds the threshold, focusing is performed by a focusing control part 320.;COPYRIGHT: (C)2007,JPO&INPIT