telescope

(redirected from refractor)
Also found in: Dictionary, Thesaurus, Legal, Encyclopedia, Wikipedia.
Related to refractor: reflector

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 ?
Whichello used a 6-inch refractor for many years which he mainly used for lunar and planetary observations.
Head of the BHVI, Professor Brien Holden, said: "The Virtual Refractor provides a realistic experience that allows optometry students to learn refraction faster, and in their own time.
Wessel Nel for the other half of the Castor & Pollux twins and a Polarex refractor with a flexion hinge Crayford focuser.
The ACIC decided to use the 24-inch [60cm] f/16 Alvan Clark planetary refractor at Lowell Observatory, which provided resolution of small lunar features that seemed to be at least as good as the 40-inch Yerkes at a location with fewer cloudy nights and adequate supporting facilities.
Like Refractor, The Holyman could pose a threat returning to Polytrack having chased home Viking Storm and Biographer in a hot handicap at Lingfield two starts ago, but Kiwayu has the much greater scope for improvement.
He has constructed and refurbished may other pieces of astronomical equipment, including a 6-inch [152mm] f/15 refractor that he used for some years for solar observations, a large equatorial mount that he used for many years, and a Herschel wedge.
Zeekoegat saw the erection of the so-called GPO (Grand Prism Objectif) telescope, a 40 cm objective-prism refractor, for determining radial velocities.
REFRACTOR confounded the layers by winning the 1m3f handicap despite getting loose and leading track staff a merry dance for several minutes as they tried to apprehend the runaway horse.
The Thomson Software controls the test chart and the computerised Nidek refractor head allows us to make more comparisons, at greater speed and so the results are likely to be more precise.
Utilizing recycled aluminum, innovative LED refractor technology, minimal battery power and compact solar panels, Radarsign driver feedback signs deliver bright, easy-to-read feedback to slow speeding drivers.
Mirror, refractor, porro, roof prism: what's the difference?
Toy Story 3[R] Playground Twist N' Fold Pop-Up Tent - $10 Disney Princess([R])Dinnerware Play Set - $10 Disney([R]) Activity Tray - $8 Barbie([R]) Mini Pets - $5 Taylor Swift([R]) Pretty Melody Fashion Collection - $10 My Very Own Kitchen - $20 Jeff Gordon Racing Trike - $15 Cat([R]) Collection - $3 - $12 Animated Dinosaur - $15 Smithsonian([R])Diggin' Up Dinosaurs[TM] T-Rex or Crystal Growing set - $10 Twilight Eclipse Game - $12 Vivitar([R]) Refractor Telescope - $20 Polaroid([R]) 2GB Music & Video Player - $25