Patent ID: 8274661

Claim:
A method for calculating a shape, the method comprising: dividing an aspherical test surface into a plurality of measurement regions configured to overlap with one another, receiving, at a light receiving unit, interference fringes which occur due to interference light generated by light reflected on a reference surface serving as a reference for calculating a shape of the test surface and light reflected by each of the measurement regions, and calculating surface shapes of the measurement regions; and calculating a shape of the test surface by joining the calculated surface shapes of the measurement regions, wherein the calculation of surface shapes of the measurement regions, includes: adjusting a position of the test surface based on the reference surface; adjusting a position of the light receiving unit so that the test surface and the light receiving unit have a conjugate relationship with each other in a state in which the position of the test surface is kept adjusted based on the reference surface; measuring phase distributions of the interference fringes in a state in which the position of the light receiving unit is adjusted; and calculating the surface shape of each of the measurement regions based on the measured phase distributions of the interference fringes.