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 SF. A signal processing part 230 outputs the focus signal SFand a received light quantity signal SAB. In a light quantity level comparison part 410, the received light quantity signal SABis compared with a light quantity level threshold 421. When the received light quantity signal SABis 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 SFis compared with a focus signal level threshold 451. In the case that the focus signal SFexceeds the threshold, focusing is performed by a focusing control part 320. COPYRIGHT: (C)2007,JPO&INPIT