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narrow-angle dark-field illumination

An imaging system designed to highlight small deviations in a planar reflective object such as a mirror. The system can be used to detect minute flaws or to image faint marks that are made in the polished surface. A ringlight is positioned concentric to and close to a telecentric lens, such that the diameter of the ringlight is only slightly larger than, and in the same plane as, the entrance pupil. If the distance between the entrance pupil and the object is at least 10 times the diameter of the entrance pupil, then the lighting will be narrow-angle dark-field illumination.
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