Exit pupil of binoculars - meaning and calculation In addition to the twilight number, the exit pupil at the eyepiece of the binoculars is also very important for seeing in twilight (twilight vision). In theory, the larger the diameter of the exit pupil, the greater the image brightness in the eye. Calculating the exit pupil To determine the binocular exit pupil, calculate the ratio of the binocular magnification to the objective lens diameter: For 8x56 binoculars, calculate the [...]