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1. An optic instrument used to visualize or photograph distant or out-of-view objects through magnification of the image or angulation of the reflected light. In medicine, usually combined with endoscopy.
2. Enclosure such that smaller segments collapse into larger.
[tele- + G. skopeō, to view]


An optical instrument for magnifying the apparent size of distant objects. It consists, in principle, of two lenses: (1) the objective, being a positive lens which forms a real inverted image of the distant object; (2) the eyepiece through which the observer views a magnified image of that formed by the objective. The eyepiece may be either positive (astronomical or Kepler telescope) or negative (galilean telescope). The magnification M of a telescope is given by the following formula
M = fo/fe
= Do/Dewhere fo is the second focal length of the objective, fe the first focal length of the eyepiece, and Do and De are the diameters of the entrance and exit pupils of the telescope (approximately equal to the diameters of the objective lens and the eyepiece).There are also some telescopes that do not use a lens (or lens system) as objective, as these are difficult to produce if large apertures and minimum aberrations are required. These telescopes use a concave mirror (usually parabolic) as the objective. They are called reflecting telescopes. Light from a distant object is collected by the large concave mirror and reflected onto a small mirror (positive in the Cassegrain telescope and negative in the gregorian telescope). This mirror is located on the optical axis and light is then transmitted through a central hole in the concave mirror onto the eyepiece. In the newtonian telescope the light collected by the large concave mirror is reflected onto a small plane mirror at a 45º angle to the optical axis, and transmitted to the eyepiece, which is at right angles to the optical axis (Fig. T1). See binoculars; eyepiece; telescopic magnification; objective.
astronomical telescope See telescope.
bioptic telescope A system of lenses forming a galilean or Kepler telescope which is mounted high on a plastic spectacle or carrier lens with the distance correction, so as to allow the patient to look through either the telescope, or below, by moving his or her head. It is used to magnify distant objects for patients with low vision. Syn. bioptic position telescope.
Cassegrain telescope See telescope.
Dutch telescope See galilean telescope.
galilean telescope A simple optical system that allows observation of far objects with a low magnification and without image inversion. It consists of a convex lens, which acts as the objective, and a concave lens as the eyepiece. Magnification of such a telescope rarely exceeds ✕ 5. This optical system is used in opera glasses and as a low vision aid (Fig. T1). Syn. Dutch telescope. See binoculars; minification.
gregorian telescope; Kepler telescope; newtonian telescope See telescope.
reflecting telescope A telescope that uses a concave mirror as the objective.
refracting telescope A telescope that uses a positive lens system as the objective.
reverse telescope See visual expander field.
terrestrial telescope A telescope that provides an erect image of a distant object. The image is usually erected by means of a lens system placed between the objective and the eyepiece. It does, however, make the terrestrial telescope relatively longer than an astronomical telescope. See binoculars; erector.
Fig. T1 Telescopes: A, galilean; B, Keplerenlarge picture
Fig. T1 Telescopes: A, galilean; B, Kepler
References in periodicals archive ?
All astronomical telescopes, large or small, share a common goal--to magnify and brighten your views of celestial bodies.
Finally, Venus will appear with the moon on February 16 and residents of Qatar will be able to watch this event over western horizon after sunrise time by using astronomical telescopes.
People in Qatar do not require astronomical telescopes to see the meteor shower.
Moreover, he said, "Uzbekistan has also pledged to set one of the largest four-metre astronomical telescopes (in OIC countries) at a cost of $60 million, while Pakistan, Iran and Kazakhstan will provide human resource for the four-year project.
the beauty of the planets using the astronomical telescopes, which will
Astronomer Francesco Di Cosimo of StarWorks based in Italy has spent the last 16 years learning about astronomical telescopes and has been very pleased to be able to help with product testing on telescopes produced by the Northek company.
Powerful astronomical telescopes and equipment will be on display and experts from the SAS will be available to answer any questions and point out the constellations.
Powerful astronomical telescopes and equipment will be on display, and experts from the SAS will be available to answer any questions and point out constellations.
Astronomical telescopes come in three basic types: refractors, which have a large lens up front to gather and focus the light; reflectors, which have a concave mirror at the bottom of the tube to do the same job, and compound (or "catadioptric") scopes that combine lenses and mirrors for a more compact design.
The MMT, located on the site of the Fred Lawrence Whipple Observatory, is one of the world's largest astronomical telescopes, located on top of the 8,530-high Mount Hopkins, south of Tucson, Arizona.
The Emirates Mobile Observatory is the first of its kind and one of the latest designs compared to other astronomical telescopes.
Tomorrow night and on Saturday, January 18 visitors to Saltholme will have the opportunity to crawl inside a portable planetarium to see the wonders of the universe projected inside, before heading outside where there will be astronomical telescopes and experts on hand to help you to spot the constellations over the reserve.

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