exit pupil

American  

noun

Optics.

1. 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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exit pupil British  

noun

1. 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

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Example Sentences

As magnification grows or the objective lens shrinks, this �exit pupil� gets smaller, which is fine in the daytime when our eyes constrict, but far less efficient at night.

From Time Magazine Archive

The component S1 of the system, situated between the aperture stop and the object O, projects an image of the diaphragm, termed by Abbe the ``entrance pupil''; the ``exit pupil'' is the image formed by the component S2, which is placed behind the aperture stop.

From Project Gutenberg