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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 ?
Analysis of Astronomical telescope Industry Key Manufacturers
Highly accurate mirrors made at the OpTIC optics technology and business incubation centre at St Asaph Business Parkare tobe used in the construction of some of theworld's biggest astronomical telescopes, each roughly the size of a football field.
Offering the industry's broadest product line of astronomical telescopes, solar telescopes, binoculars, microscopes and related optical accessories, the company distributes its products worldwide through a network of specialty retailers, mass merchandisers and domestic and foreign distributors.
Peter Wise is now competing with multi-million pound companies in the production of astronomical telescopes from his workshop base on St Asaph Business Park.
Thousands of the segments will be needed for future astronomical telescopes such as the European Extremely Large Telescope.
Wavefront-guided custom ablation, or simply custom LASIK, is based on technology first used in ground-based astronomical telescopes for measuring and correcting the aberrations of the atmosphere.
The observatory is a proposed member to operate a new generation of astronomical telescopes, envisioned to dwarf the world's largest telescopes.
Bushnell also markets binoculars, astronomical telescopes, laser rangefinders and spotting scopes under the Bushnell brand.
The development of optical engineering and in particular the design and construction of optical instruments has always been an important part of his activities, among which we may mention several astronomical telescopes and many optical testing instruments.
was established in 1926 by Seizo Goto to produce astronomical telescopes, later expanding to include planetarium and hemispheric film projectors.
Working in strategic partnership with major retailers and mass merchandisers -- with whom we have so successfully marketed less expensive astronomical telescopes -- to concentrate on binoculars and spotting scopes will be Brent's first order of business.
Kodak C&GS also has created primary mirrors for the world's largest ground-based astronomical telescopes.

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