telescope

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tel·e·scope

(tel'ĕ-skōp),
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]

telescope 

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 classic literature ?
But if he elects to attempt it, let him be warily careful of two things: chose a calm, clear day; and do not pay the telescope man in advance.
Before they had had time to traverse the "Corridor" and reappear, twilight was come, and the power of the telescope was at an end.
Sometimes, whilst covering Van Baerle with his telescope, he deluded himself into a belief that he was levelling a never-failing musket at him; and then he would seek with his finger for the trigger to fire the shot which was to have killed his neighbour.
But others are dreaming of the day the telescopes will be torn down.
Innovative Line of Telescopes Transforms Any Backyard into a Neighborhood Observatory as SkyAlign[TM] Technology, Automated Sky Tours, and a 40,000 Celestial Object Database Make Astronomy Simple for All
The book recounts the rise of facilities housing telescopes of unprecedented size and craftsmanship and the development of satellite telescopes, such as the famous Hubble Space Telescope.
6 million miles, observers with simple amateur telescopes and clear skies had the chance to get spectacular views of Mars.
BIG RESEARCH TELESCOPES HAVE ALWAYS been expensive, partly because each one is an individually crafted item.
Yet for all its dazzle, you won't see the Pistol Star with your naked eye, or even through the most powerful telescopes on Earth.
Federal Lawsuit Seeks An Injunction Preventing Meade And Fourteen of Its Distributors From Falsely Advertising Its RCX400 and LX200R Meade Telescopes As Having An Advanced "Ritchey-Chr[c]tien" Design
The observations indicate that in an even earlier epoch, one whose denizens are now too far away and too dim to be seen by existing telescopes, some galaxies were "furiously luminous" and teeming with new stars, says Ellis.
When the full moon darkens during Thursday night's total eclipse, sidewalk astronomers can get a front-row seat through telescopes set up outside the Griffith Observatory Satellite in the northeast corner of Griffith Park.