Exit Pupil of an Optical System

The exit pupil is a virtual aperture in an optical system through which all the rays of light exiting the system pass. It is located at the image plane and is an important parameter for systems such as telescopes and binoculars. In this formula, P represents the exit pupil diameter, objectiveDiameter is the diameter of the front lens of the system (also known as the aperture), and magnification is the magnifying power of the system. The exit pupil diameter is inversely proportional to the magnification, meaning higher magnifications yield smaller exit pupils. The value is expressed in the same units used for the objective diameter (e.g., millimeters).