Definition of exit pupil in English:

exit pupil

noun

  • The image of the aperture stop formed by rays of light after they have passed through an optical system, specifically the bright disk visible through the eyepiece when an optical instrument (such as a camera, telescope, gunsight, etc.) is directed towards a light source; the diameter of this image.

Origin

Late 19th century; earliest use found in Journal of the Royal Microscopical Society.