About Fit My Telescope

Telescope eyepiece and mount fitment: magnification, true field, exit pupil, payload

An eyepiece does not have a magnification of its own. The number you get depends on the telescope it goes in. Start from your telescope or from an eyepiece and get the exact magnification, true field of view and exit pupil the pair produces, whether it sits inside the telescope's useful range, the barrel size that has to match, and the mount payload and camera-adapter thread that decide what else will fit.

Figures are compiled from Celestron, Sky-Watcher and Orion manufacturer specification pages and from retailer spec tables at High Point Scientific, Astronomics, OPT and Agena Astro, cited on each page. The optical formulas (magnification = telescope focal length divided by eyepiece focal length, true field = apparent field divided by magnification, exit pupil = aperture divided by magnification, highest useful magnification = about 2x the aperture in millimetres) are standard and shown on each resolution page.

Aperture, focal length, focal ratio, eyepiece focal length, apparent field of view and barrel size are quoted from published manufacturer specification sheets, cited on each page. Magnification, true field of view, exit pupil and highest useful magnification are then computed from those figures with the standard optical formulas, also shown on each page so you can check the arithmetic. Confirm your own telescope's focal length and your eyepiece's focal length and barrel before buying, because a telescope sold under one name can ship with a different focal length across model years.

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