Astrophysics (index)

Exit Pupil

(size of the image as presented to the eye)

The Exit Pupil of a telescope (or binoculars or microscope or other optical device) is where it is designed that your eye should go to look through it. It is a disk through which the image is projected, some distance from the eye piece (the Eye Relief) so that despite the physical characteristics of the instrument, the eye lens can be brought to the exit pupil. The size of the exit pupil (Pupil Size) is best sized to the pupil of the eye, which is at its maximum with night vision and is larger for young adults than older adults. If an ill-designed instrument does not allow your eye lens to line up with the exit pupil, parts of the image can be blurred.