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 periodicals archive ?
Refracting telescopes uses lenses to make faraway objects look closer so we can see them in greater detail.
When he was young Bopp began observing with a department-store refracting telescope that "didn't amount to anything but disappointment," he says.
The sky looked promising on the evening of March 30, 1996, as more than a dozen representatives from various astronomy clubs in the Northeast gathered in Hadley, Massachusetts, to witness the first light of a newly reconstructed refracting telescope.
Barlow Pepin is currently writing a book on the refracting telescope for Cambridge University Press.
When Lick Observatory opened in June 1888 it boasted the largest refracting telescope in the world - a 36-inch Clark.
These can be seen in any competently made refracting telescope.
Occupying a corner of my home garden in Deltona, Florida, and equipped with a 6-inch D & G refracting telescope, this is the only full-time solar observatory in the Sunshine State.
To Flammarion, the telescope's success was further evidence that "the future lies in the development of refracting telescopes rather than reflecting.
Refracting telescopes focus red and blue lights differently.
Binoculars are essentially two refracting telescopes fixed together.
We are especially encouraged by the fact that our new digital technology -- incorporated in the recently introduced ETX-90EC with the hand-held Autostar computer controller -- has been enthusiastically received and is being applied to our entire family of less-expensive refracting telescopes.