Before revision: Telescopes The small exit pupil of a 25×30 telescope and large exit pupils of low light use capable 9×63 binoculars For a telescope, the diameter of the exit pupil can be calculated by dividing the focal length of the eyepiece by the focal ratio (f-number) of the telescope.
After revision: Telescopes The small exit pupil of a 25×30 telescope and large exit pupils of suitable for use in low light 9×63 binoculars For a telescope, the diameter of the exit pupil can be calculated by dividing the focal length of the eyepiece by the focal ratio (f-number) of the telescope.