Patent ID: 7423739

Claim:
A method of determining the aberration of an optical imaging system, which method comprises the steps of: arranging a test object in the object plane of the imaging system; forming a number of test object images by means of the imaging system and an imaging beam, each test object image being formed with another focus state of the imaging system; detecting the test object image by means of a detection device having a resolution larger than that of imaging system, and analyzing an output signal of the detection device to determine values of different aberration terms of the aberration, characterized in that the step of arranging the test object comprises including at least one test object feature having a size small compared to the resolution of the imaging system; the step of detecting the test object image comprises detecting for all images of a test object features the intensity profile across the whole image plane area associated with this test object feature, which image plane area is substantially larger than the first ring of the Airy distribution of the image of the test object feature, and the step of analyzing comprises solving at least one set of equations including radial parts of point spread functions, which result from the different aberration terms, to retrieve these aberration terms.