Patent ID: 8077391

Claim:
A mask used in a wavefront aberration measuring device in which wavefront aberration of a to-be-tested optical system is measured, the mask comprising: a pattern including a pinhole producing a spherical wave, a plurality of diffraction gratings adjoining each other and each ruled with lines oriented in a direction different from the other diffraction grating, wherein the mask is placed in an object plane of the to-be-tested optical system wherein the wavefront aberration is measured based on interference fringes produced by applying light from a light source to the pattern so as to cause the light emitted from the pattern to be split after being transmitted through the to-be-tested optical system, wherein the plurality of diffraction gratings include: two diffraction gratings adjoining in a first direction and each ruled with lines oriented in a direction different from those of the other diffraction grating; and two diffraction gratings adjoining in a second direction perpendicular to the first direction and each ruled with lines oriented in a direction different from those of the other diffraction grating, wherein the position of a boundary between the two diffraction gratings adjoining in the first direction matches a position of a center of the pattern in the first direction, and wherein a boundary between the two diffraction gratings adjoining in the second direction lies at a predetermined distance from the center of the pattern in the second direction.