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1 December 2008 15:21
- the part of a telescope (or binoculars) into which you (typically) look
- a.k.a. "ocular" or (less commonly) "ocular lens;" often abbreviated EP
- telescope eyepieces are typically removable, binocular eyepieces typically are not
- many telescopes (refractors, Newtonian reflectors) achieve focus by moving the eyepiece by means of a mechanical focuser forwards or backwards in the light cone near the focal point of the telescope's objective
- on some binoculars, both eyepieces are focusable via helical focusers, on others only one eyepiece can be adjusted (a diopter adjustment)
- common eyepiece designs include: Plössl, orthoscopic (Abbe), Kellner, and Erfle
- some eyepiece designs are patented and/or the name is trademarked, e.g., TeleVue's Radian, Panoptic, Nagler, and Ethos lines
- the focal length (FL) of the eyepiece determines the magnification of the view through a given telescope; the lower the eyepiece FL, the higher the magnification: magnification = telescope's FL / eyepiece's FL
- for better viewing positions, eyepieces are generally placed in diagonals on cadioptric and refractor telescopes
- common barrel sizes for eyepieces are 1.25 inches and 2 inches. Less common (and typically now only found on lower quality scopes) are 0.965 inch barrels.
- some eyepiece barrels have "safety cutouts" so set screws will hold them more securely; they can be a liability for people who have accessories (diagonals/focusers/visual backs) with compression rings as the cutouts sometimes "hang" on the compression rings
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Orion Telescopes
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