entrance pupil

American  

noun

Optics.

1. the image of the aperture viewed from the objective of an optical system limiting the rays that enter the system.

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Example Sentences

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

Since the maximum aperture of the pencils issuing from O is the angle u subtended by the entrance pupil at this point, the magnitude of the aberration will be determined by the position and diameter of the entrance pupil.

From Project Gutenberg

This distance replaces the angle u in the preceding considerations; and the aperture, i.e. the radius of the entrance pupil, is its maximum value.

From Project Gutenberg