exit pupil

**exit pupil**
The exit pupil is the small, bright circle of light visible when you look through an optical instrument like binoculars, microscopes, or telescopes. It represents the image of the aperture stop as seen from the rear of the system, effectively showing where your eye should be positioned to see the full field of view. Understanding the exit pupil is important for optimizing comfort and clarity when using optical devices. A larger exit pupil generally makes it easier to use the instrument in low light or when your eye is not perfectly aligned.