refracting telescope


Also found in: Dictionary, Thesaurus, Medical, Legal, Wikipedia.

refracting telescope

a type of telescope in which the image is formed by a set of lenses

refracting telescope

(ri-frakt -ing) (refractor) A telescope employing an objective lens to bring the light rays to a focus. The first telescopes were simple refractors with single-lens objectives: these were the Galilean and Keplerian telescopes, introduced in the early 17th century. They were supplanted by reflecting telescopes in the last quarter of that century because no-one at that time could overcome their chromatic aberrations, which introduced brilliant false color effects in the images. Although John Dollond discovered how to make an achromatic lens in 1756, he could make only small diameters suitable for terrestrial telescopes; glass makers did not know how to make large uniform disks of crown and flint glass. This obstacle was overcome in the early 1800s by Joseph Fraunhofer, who made the 24-cm refractor at Dorpat and the 16-cm heliometer at Königsberg. His successor, Georg Merz, supplied the 32.4-cm equatorial refractor to the Royal Greenwich Observatory and manufactured the 38-cm refractor that was the first large telescope to be mounted in the USA, at Cambridge, Massachusetts, in 1847.

For years after this, American astronomers leaned strongly toward the refractor. By the 1880s Alvan Clark was making relatively large refractors: a 47-cm diameter instrument for the Dearborn Observatory, a 91-cm one for Lick Observatory, and a 102-cm one for Yerkes Observatory. Other very large refractors built in the late 19th century are the 61-cm at both Lowell Observatory, Arizona, and the Pic du Midi in France, the 75-cm at Pulkovo Observatory, St Petersburg, and the 83-cm at the Meudon Observatory in Paris. There are great technical problems in making large lenses free of imperfections and impurities, and of supporting these lenses (only around the edge) so that distortion of the image is minimal. The desire for ever larger apertures to reach ever farther and fainter objects in space has meant that the major telescopes built in the 20th and 21st centuries have been reflectors.

The surviving large refracting telescopes are mainly used in astrometry for the measurement of stellar positions, proper motions, and parallax. Refractors are often preferred by visual observers because of their long focal length and closed tube; the latter avoids air currents in the tube, which often cause an unsteady image.

refracting telescope

[ri′frak·tiŋ ′tel·ə‚skōp]
(optics)
A telescope in which a lens gathers light and forms a real image of an object. Also known as refractor telescope.
References in periodicals archive ?
In 1897 Clark, the discoverer of Sirius's dim companion (see 1844), supervised the construction of a refracting telescope with a lens 40 inches across.
Market Growth by Types: Refracting Telescope, Reflector Telescope & Catadioptric Telescope
Groups of curious people peered through the refracting telescope set up on the steps of the Burj Khalifa.
Telescope makers both amateur and professional may be interested in a new refracting telescope concept I have evolved over two years of intensive research.
Aldrich, who graduated from Worcester Academy and Brown, became interested in astronomy after the Class of 1897 gave the academy a refracting telescope in 1907.
Members of the public will be able to book sessions on the observatory's 28-inch refracting telescope on selected nights.
The eyepiece of a refracting telescope is a magnifier.
IN A REFRACTING TELESCOPE, THE OBJECTIVE IS A LENS ASSEMBLY.
View planets in our solar system through a classic Victorian refracting telescope. Also on Sun-Fri.
38), the photograph of William Huggins seated with a refracting telescope caught my eye.
Scientific instruments are well represented with a selection of barometers, globes, sundials, microscopes and telescopes led by a very large 4.5 inch refracting telescope dating to around 1900.