A lens system, also known as an ocular, used to magnify the image formed by the objective of a telescope.
From → eye + piece, from O.Fr. pièce, from V.L. *pettia, probably from Gaulish (cf. Welsh peth "thing;" Breton pez "piece"), from O.Celt. base *pett-.
Cašmi "ocular," adj. of cašm→ eye + -i adj. suffix.
cešmi-ye Kellner (#)
Fr.: oculaire de Kellner
The first achromatic eyepiece consisting of a convex lens and a plano-convex lens. The convex surfaces are turned toward one another.
Named after the inventor Carl Kellner (1826-1855), a German engineer and optician; → eyepiece
Fr.: oculaire orthoscopique
A telescopic eyepiece that produces a wide field of view (between 40° and 50°). The eyepiece consists of a single element lens that is normally plano-convex, and a cemented triplet that is usually symmetrical.
cešmi-ye Ramsden (#)
Fr.: oculaire de Ramsden
An eyepiece consisting of two planoconvex lenses of the same focal length, placed with the convex sides facing each other and with a separation between the lenses of about two-thirds of the focal length of each.
Named after Jesse Ramsden (1735-1800), English maker of astronomical instruments; → eyepiece.