Before revision: The exit pupil is an image (real or virtual) of the aperture made by the optics following it; divergent rays from each point in the aperture plane come together again (focused) in the exit pupil.|330x330px To use an optical instrument, the entrance pupil of the viewer's eye must be aligned with and be of similar size to the instrument's exit pupil.
After revision: The exit pupil is an image of the aperture made by the optics following it; divergent rays from each point in the aperture plane come together again in the exit pupil.|330x330px To use an optical instrument, the entrance pupil of the viewer's eye must be aligned with and be of similar size to the instrument's exit pupil.