Patent ID: 7518735

Claim:
A measurement method for measuring a wavefront aberration of a target optical system using an interference pattern formed by a light from a first image side slit and a light from a second image side slit, the first and second image side slits being located at an image side of the target optical system, the first image side slit having, in a shorter direction, a width equal to or smaller than a diffraction limit of the target optical system, and the second image side slit having, in a shorter direction, a width greater than the diffraction limit of the target optical system, said measurement method comprising the steps of: obtaining four or more primary wavefronts of the target optical system from different measurement directions; and calculating a wavefront aberration of the target optical system based on the four or more primary wavefronts of the target optical system obtained by said obtaining step wherein said obtaining step includes steps of: obtaining a first primary wavefront of the target optical system in a first measurement direction; obtaining a second primary wavefront of the target optical system in a second measurement direction orthogonal to the first measurement direction; obtaining a third primary wavefront of the target optical system in a third measurement direction that inclines by 45° to the first measurement direction; and obtaining a fourth primary wavefront of the target optical system in a fourth measurement direction orthogonal to the third measurement direction, wherein said calculating step includes steps of: calculating a first wavefront based on the first and second primary wavefronts; calculating a second wavefront based on the third and fourth primary wavefronts; and calculating a wavefront of the target optical system based on the first and second wavefronts.