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entrance pupil

noun, Optics.
the image of the aperture viewed from the objective of an optical system limiting the rays that enter the system.
Compare exit pupil. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for entrance pupil
  • Also, the incandescent arc of the lamp must fill the entrance pupil of the condenser.
  • The ratio of the effective focal length of an optical system to the diameter of the entrance pupil.

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