Partial coherence mitigation in video measurement systems via illumination apodization

A method of measuring a test object comprising:

• (a) presenting a test object within a video measuring system, the video measuring system having an imaging system and an illumination system;
• (b) emitting an illumination distribution of light along an optical path with the illumination system, the illumination system comprising an illumination lens and a subassembly having an illumination source, a pupil aperture, and a first polarizer, the first polarizer having a diameter that is smaller than the pupil aperture;
• (c) capturing at least a portion of a silhouette of a test object with an imager having an imaging pupil by receiving light transmitted by the test object;
• and
• (d) rotating a second polarizer independent of and relative to the subassembly to change a ratio of illumination passing through both the first and second polarizer,
• wherein the second polarizer (i) has a diameter that is larger than the first polarizer and (ii) overlaps the first polarizer.

A video measurement system for measuring a test object comprising:

• an imaging system comprising an imager having an imaging pupil, the imager arranged for viewing at least a portion of a silhouette of a test object by receiving light transmitted by the test object over a first angular extent;
• an illumination system, the illumination system comprising an illumination source emitting an illumination distribution of light along an optical path, an illumination lens, a second angular extent that is larger than the first angular extent received by the imager, and an output, wherein the pupils of the illumination and imaging systems are in conjugate image planes;
• a subassembly within the illumination system, the subassembly comprising a pupil aperture and a first polarizer, the first polarizer having a diameter that is smaller than the pupil aperture;
• and
• a second polarizer overlapping the first polarizer, the second polarizer having a diameter that is larger than the first polarizer, the second polarizer configured to rotate independent of and relative to the subassembly.