Patent ID: 8363227

Claim:
A measurement apparatus which measures a wavefront of light traveling from a member to be measured, the apparatus comprising: a first reference surface; a second reference surface configured to function as a reference surface for said first reference surface; an optical system configured to form a first interference pattern of light traveling from the member to be measured and light traveling from said first reference surface, and a second interference pattern of light traveling from said first reference surface and light traveling from said second reference surface; a detection unit configured to detect the first interference pattern and the second interference pattern, respectively; and a calculation unit configured to calculate a change amount of a wavefront of light traveling from said first reference surface based on the second interference pattern detected by said detection unit, when the change amount of the wavefront falls outside an allowable range, calculate a wavefront of light traveling from the member to be measured by removing, from a wavefront calculated based on the first interference pattern, a wavefront error arising from said optical system and the change amount of the wavefront of light traveling from said first reference surface, and when the change amount of the wavefront falls within the allowable range, calculate the wavefront of light traveling from the member to be measured by removing, from the wavefront calculated based on the first interference pattern, the wavefront error arising from said optical system.