Patent ID: 8462351

Claim:
An apparatus which measures a wavefront aberration of an optical system, the apparatus comprising: a reflector configured to reflect a light traveling from the optical system, an angle of an optical axis of the reflector being variable relative to a gravity direction; a measurement optical system configured to include one of a reference surface or a wavefront conversion element; a detector configured to detect a light incident thereon via the reflector and the measurement optical system including the one of the reference surface or the wavefront conversion element; and a load application device configured to: apply a load to the reflector in an application direction perpendicular to the optical axis, the load application device applying a compression load to a first portion of the reflector below the optical axis, at a magnitude corresponding to the angle and a position of the first portion, in the application direction thereat; and apply a tension load to a second portion of the reflector above the optical axis, at a magnitude corresponding to the angle and a position of the second portion, in the application direction thereat.