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 ?
I gave that man some spiritual advice and disposed of him, and then paid the telescope man his full fee, and said that we were charmed with the trip and would remain down, and not reascend and require him to fetch us down by telescope.
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.
Is it against the law to use a telescope in Portsmouth?"
In the middle of the hut a flat stone served the purpose of a table, and upon this stood a small cloth bundle--the same, no doubt, which I had seen through the telescope upon the shoulder of the boy.
Chile's Las Campanas Observatory already hosts the twin Magellan Telescopes, each bearing a 6.5-meter (21-foot) mirror.
The ESPRESSO instrument on ESOs Very Large Telescope in Chile has for the first time been used to combine light from all four of the 8.2-metre Unit Telescopes.
The observations will include data from all four of the telescopes' science instruments on-board.
The first ever picture of a dark hole for this situation the one at the core of our universe will be pieced together utilizing the information or data gathered by a network of telescopes extending from Hawaii to Antarctica to Spain for five evenings running.
This article outlines the practical applications of telescopes and how these devices should be integrated into low vision practice for the benefit of our patients.
Optical telescopes, when pointed at distant objects, make things appear closer, larger or brighter to our eyes.