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A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and astronomical telescopes but is also used for long-focus camera lenses .
Lens sag is a problem that sometimes afflicts very large refracting telescopes. It is the equivalent of mirror sag in reflecting telescopes. It occurs when the physical weight of the glass causes a distortion in the shape of the lens because the lens can only be supported by the edges. A mirror on the other hand can be effectively supported by ...
This article is a list of notable unsolved problems in astronomy. Problems may be theoretical or experimental. Theoretical problems result from inability of current theories to explain observed phenomena or experimental results. Experimental problems result from inability to test or investigate a proposed theory.
The Swedish 1-m Solar Telescope, with a lens diameter of 43 inches, is technically the largest, with 39 inches clear for the aperture.The second largest refracting telescope in the world is the Yerkes Observatory 40 inch (102 cm) refractor, used for astronomical and scientific observation for over a century.
The telescope was placed by the astronomer James William Grant, and it had an 11-inch aperture (280mm) and a 16 feet (4.88m) focal length. [16] [17] At the 1861 International Exhibit, the size increased to showing a telescope with 21-inch objective lens. [18] The Buckingham or Walworth Common telescope's objective was manufactured by William ...
Two-element refracting telescopes were extensively used in 19th century observatories despite their smaller apertures than metal, and later glass, mirror telescopes. The technology for silver-coating glass mirrors, more reflective than speculum metal and not subject to tarnishing, was developed in the mid-19th century but was slow to be adopted.
Alvan Clark & Sons was an American maker of optics that became famous for crafting lenses for some of the largest refracting telescopes of the 19th and early 20th centuries. Founded in 1846 in Cambridgeport, Massachusetts , by Alvan Clark (1804–1887, a descendant of Cape Cod whalers who started as a portrait painter), and his sons George ...
Notes written by Thomas Digges in the publication of the book Pantometria in 1570 contain descriptions of how Leonard Digges made use of a "proportional Glass" to view distant objects and people. Some, such as astronomer and historian Colin Ronan , claim this describes a reflecting or refracting telescope built between 1540 and 1559, but its ...