Bertrand lens

A lens that, when inserted in the optical path, allows for the observation of the aperture set of conjugate planes and, in polarized light microscopy, the conoscopic interference pattern.

See also: Bertrand diaphragm, aperture plane, conoscopic interference pattern, phase telescope

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Conjugate Planes in Optical Microscopy

Image-forming and aperture planes form two independent focal sets in the optical train.