The point on an elliptic orbit at the greatest distance from the principal focus. Also knwon as → apocenter.
kânun-e Cassegrain (#)
Fr.: foyer Cassegrain
The main focus in → Cassegrain telescope.
kânun-e ârenjvâr, ~ kudé
Fr.: foyer coudé
An → optical system in which the → beam of light from the → primary mirror is reflected down through the instrument's → polar axis by a path bent like an → elbow. Since the focus remains fixed with respect to the Earth, light can be analyzed with permanently installed instruments. In addition long → focal lengths allow higher → spectral dispersions.
From Fr. coudé "elbowed," from coude "elbow," L. cubitus; → focus.
To cause to deviate from accurate focus.
1) kânun; 2) kânunidan
Fr.: 1) foyer; 2) focaliser
1) (n.) A point where parallel light rays from an object are gathered together by a
lens or a concave mirror. It is the place where the clearest image of a distant object
forms. Also called focal point. See also → focal distance.
From L. focus "hearth, fireplace," of unknown origin,
Kânun "hearth, fireplace."
Of an optical system, being in focus or brought into focus; adjusted to produce a clear image.
Past participle of → focus.
The act of bringing into focus.
Noun of → focus.
kânun-e Nasmyth (#)
Fr.: foyer Nasmyth
In an altazimuth-mounted telescope, a focal point to one side of the tube, created by placing a third deflecting mirror in the optical path. This extra mirror directs the beam along the altitude axis, and through a hole in the supporting trunnions. Nasmyth focus has the advantage of remaining at a fixed position relative to the telescope wherever the instrument is pointed. Moreover, bulky or heavy instruments can be mounted there on a permanent platform, which rotates only in azimuth.
Named after the inventor James Nasmyth (1808-1890), who first used it in the 19-th century.
kânun-e Newton, ~ Newtoni
Fr.: foyer de Newton
The focus obtained by diverting the converging light beam of a reflecting telescope to the side of the tube.
Fr.: foyer primaire
The focal point of a large primary reflecting mirror. This focus actually falls at a point just within the upper structure of the telescope and provides a large field of view.