the ridge of the entrance pupil of an optical system, indicating the place where the pupil of the eye should be placed to view the object.
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Also called eye point.
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British Dictionary definitions for exit pupil
the smallest cross section of the beam of light from the eyepiece of a telescope through which all the light from the eyepiece passes. Its diameter is equal to the ratio of the focal length of the eyepiece to the focal ratio of the telescope
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012