The exit pupil is the width of the cone of light leaving the eyepiece, and matching it to your own eye pupil is the secret to bright, comfortable views. It equals the aperture divided by the magnification, or equivalently the eyepiece focal length divided by the telescope focal ratio. A large exit pupil near seven millimeters gives the brightest possible deep sky image but only if your dark adapted pupil is that wide, otherwise light is wasted. A small exit pupil around half a millimeter suits high power planetary work. This calculator computes the exit pupil for any eyepiece and flags whether it is too large for a typical adult eye, all in your browser.
The exit pupil is the width of the cone of light leaving the eyepiece, and matching it to your own eye pupil is the secret to bright, comfortable views. It equals the aperture divided by the magnification, or equivalently the eyepiece focal length divided by the telescope focal ratio.
Yes. Telescope Exit Pupil Calculator is completely free, with no sign-up and no usage limits.
Yes. Telescope Exit Pupil Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Telescope Exit Pupil Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.