Patent ID: 8570532

Claim:
A noncontact surface shape measuring method for carrying out autofocusing control by way of a laser probe in an up-down direction with respect to a surface of a work, continuously scanning the work in a horizontal direction, and measuring a surface shape of the work according to a displacement amount in the up-down direction of an objective lens in an autofocusing optical system that is controlled so that a return beam of the laser probe is received at the center of a two-piece sensor, the noncontact surface shape measuring method comprising: detecting a voltage difference between two sensors of the two-piece sensor and detecting whether or not the detected voltage difference is within a neighborhood range in which a voltage difference is substantially proportional to a displacement from an in-focus position; calculating, if the detected voltage difference is within the neighborhood range, a correction value for a position of an objective lens in the up-down direction with respect to the in-focus position; and adding the correction value to an actual position of the objective lens in the up-down direction, to calculate a movement amount of the objective lens in the up-down direction.