Shape calculation method

A method for manufacturing an optical element, the method comprising:

• calculating a shape of an optical element according to a shape calculation method;
• and
• processing the optical element based on the calculated shape of the optical element,
• wherein the shape calculation process includes:
• 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.