Online Dictionary

Aplanatic telescope Explained

Aplanatic telescope at English => English (Websters 1913) Of Explained:

Telescope \Tel"e*scope\, n. [Gr. ? viewing afar, farseeing; ?
far, far off + ? a watcher, akin to ? to view: cf. F.
t['e]lescope. See {Telegraph}, and {-scope}.]
An optical instrument used in viewing distant objects, as the
heavenly bodies.

Note: A telescope assists the eye chiefly in two ways; first,
by enlarging the visual angle under which a distant
object is seen, and thus magnifying that object; and,
secondly, by collecting, and conveying to the eye, a
larger beam of light than would enter the naked organ,
thus rendering objects distinct and visible which would
otherwise be indistinct and or invisible. Its essential
parts are the object glass, or concave mirror, which
collects the beam of light, and forms an image of the
object, and the eyeglass, which is a microscope, by
which the image is magnified.

{Achromatic telescope}. See under {Achromatic}.

{Aplanatic telescope}, a telescope having an aplanatic

{Astronomical telescope}, a telescope which has a simple
eyepiece so constructed or used as not to reverse the
image formed by the object glass, and consequently
exhibits objects inverted, which is not a hindrance in
astronomical observations.

{Cassegrainian telescope}, a reflecting telescope invented by
Cassegrain, which differs from the Gregorian only in
having the secondary speculum convex instead of concave,
and placed nearer the large speculum. The Cassegrainian
represents objects inverted; the Gregorian, in their
natural position. The Melbourne telescope (see Illust.
under {Reflecting telescope}, below) is a Cassegrainian

{Dialytic telescope}. See under {Dialytic}.

{Equatorial telescope}. See the Note under {Equatorial}.

{Galilean telescope}, a refracting telescope in which the
eyeglass is a concave instead of a convex lens, as in the
common opera glass. This was the construction originally
adopted by Galileo, the inventor of the instrument. It
exhibits the objects erect, that is, in their natural

{Gregorian telescope}, a form of reflecting telescope. See
under {Gregorian}.

{Herschelian telescope}, a reflecting telescope of the form
invented by Sir William Herschel, in which only one
speculum is employed, by means of which an image of the
object is formed near one side of the open end of the
tube, and to this the eyeglass is applied directly.

{Newtonian telescope}, a form of reflecting telescope. See
under {Newtonian}.

{Photographic telescope}, a telescope specially constructed
to make photographs of the heavenly bodies.

{Prism telescope}. See {Teinoscope}.

{Reflecting telescope}, a telescope in which the image is
formed by a speculum or mirror (or usually by two
speculums, a large one at the lower end of the telescope,
and the smaller one near the open end) instead of an
object glass. See {Gregorian, Cassegrainian, Herschelian,
& Newtonian, telescopes}, above.

{Refracting telescope}, a telescope in which the image is
formed by refraction through an object glass.

{Telescope carp} (Zo["o]l.), the telescope fish.

{Telescope fish} (Zo["o]l.), a monstrous variety of the
goldfish having very protuberant eyes.

{Telescope fly} (Zo["o]l.), any two-winged fly of the genus
{Diopsis}, native of Africa and Asia. The telescope flies
are remarkable for having the eyes raised on very long

{Telescope shell} (Zo["o]l.), an elongated gastropod
({Cerithium telescopium}) having numerous flattened

{Telescope sight} (Firearms), a slender telescope attached to
the barrel, having cross wires in the eyepiece and used as
a sight.

{Terrestrial telescope}, a telescope whose eyepiece has one
or two lenses more than the astronomical, for the purpose
of inverting the image, and exhibiting objects erect.