APPROXIMATING METHOD OF OPTICAL SURFACE, AND PRISM ANGLE MEASURING METHOD USING THE SAME

PROBLEM TO BE SOLVED: To provide a method for approximating an optical surface, that is capable of approximating a shape of an optical surface with high accuracy even if there is a wave in the optical surface, and to provide a method for measuring a prism angle using the approximating method. SOLUTION: With a laser shape-measuring device 2, positions of a plurality of measurement points M on one prism surface 11 of a prism 1 are measured, and positions of a plurality of measurement points N on another prism surface 12 are measured with the prism 1 rotated. From the whole range of measurement of each prism surface, such a range is extracted as a computing range, that arranges only measuring points that satisfy the following: a distance P between the measurement points is 1 μm or more and 40 μm or less, and the measurement points satisfy the formula (1): P×β≤10 (unit: μm°) where β is a crossing angle formed by a first virtual straight line passing through the particular measurement point and a measurement point adjacent to the particular measurement point in one direction and a second virtual straight line passing through the particular measurement point and a measurement point adjacent to the particular measurement point in another direction. Based on the obtained position data of a plurality of measurement points M, N, approximate straight lines each representing one prism surface 11 and another prism surface 12 are determined, and a prism angle α formed by one prism surface 11 and another prism surface 12 is computed from a relative position to a reference line between these approximate straight lines. COPYRIGHT: (C)2009,JPO&INPIT