Wikipedia
A refracting or refractor telescope is a type of optical telescopeoptical telescope which refractionrefracts light at each end using lens (optics)lenses. This refraction causes parallel light rays to converge at a focal point; while those which were not parallel converge upon a focal plane. This can enable a user to view a distant object as if it were brightnessbrighter, clarityclearer, and/or sizelarger. These are similar to microscopes. The monocular is a type of refractor. A typical refractor has two lenses, an objective lens and an eyepieceeyepiece lens. The objective lens has two pieces of glass (with different densitydensities), "crown glasscrown" and "flint glass". Each side of each piece is ground and polishingpolished, and then the two pieces are glued together. The curvatures are designed to limit the effects of chromatic aberrationchromatic and spherical aberration.
Technical difficulties - Refractors are criticized for their relatively high-degree of chromatic aberrationchromatic and spherical aberration. There is also the problem of lens sagging, a result of gravity affecting glass. There is a further problem of mis-refraction; caused by air bubbles trapped within the lenses. In addition, glass is opacityopaque to certain wavelengths, and even optical spectrumvisible light is dimmed when it passes through glass. Many of these problems are avoided by using reflecting telescopes.However modern designs using apochromatic optics with low dispersion glass greatly reduce these problems. Such telescopes contain elements of fluorite in the objective elements and produce a very crisp image which is virtually color aberration free. Such telescopes are sold in the high-end amateur telescope market up to 150mm in diameter.
Notable refracting telescopes - Yerkes Observatory (102cm) Swedish Solar Telescope (100cm) Lick Observatory (91cm) Paris Observatory (83cm + 62cm) Nice Observatory !(76cm)Image:Tel escope.jpg''The 50 centimetrecm refractor at Nice !Observatory.''Image:TwentyInch Telescope.JPG20 inch refractor at the Observatories at Chabot Space and Science Center in Oakland, !California.Image:EightInchTele scope.JPG8 inch refractor at the Observatories at Chabot Space and Science Center in Oakland, !California.
See also - List of largest optical refracting telescopes, from which it is clear that their heyday was in the 19th century Maksutov !telescopeCategory:Telescopesde :Linsenfernrohres:Telescopio? !refractoreo:Refraktorofr:Lunet teru:Рефрактор DEBUG REDIRECT (refracting telescope)
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Astronomy and Astrophysics
A skygazing department in the Division of Physical Sciences.
http://astro.uchicago.edu/
Woodland Hills Camera & Telescopes
Large selection of binoculars, cameras, telescopes and accessories made by Meade, Celestron, TeleVue and other manufacturers.
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Wide range of outdoor gear and accessories.
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Anacortes Telescope and Wild Bird
Telescopes and binoculars by Takahashi, TeleVue, SBIG, DayStar, Celestron, Meade, Leica, Zeiss, Optec, and Canon.
http://www.buytelescopes.com/
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