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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 .
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.
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.
Primary lens: The objective of a refracting telescope. Primary mirror: The objective of a reflecting telescope. Corrector plate: A full aperture negative lens placed before a primary mirror designed to correct the optical aberrations of the mirror. Schmidt corrector plate: An aspheric-shaped corrector plate used in the Schmidt telescope.
This had an objective made by the makers Chance, with the overall telescope made by Thomas Cooke. [21] The telescope was made for Robert Stirling Newall, and when completed in 1869 was the largest refracting telescope in the world. [21] In the 1950s the University of Cambridge donated the Newall telescope to the National Observatory of Athens ...
The glass blanks for what would become Yerkes Great Refractor were made in Paris, France by Mantois and delivered to Alvan Clark & Sons in Massachusetts where they were completed. [12] Clark then made what would be the largest telescope lens ever crafted and this was mounted to an Equatorial mount made by Warner & Swasey for the observatory. [12]
A drawing of the telescope from an astronomy book. The fabrication of the two-element achromatic objective lens, the largest lens ever made at the time, caused years of delay. [2] The famous large telescope maker Alvan Clark, was in charge of the optical design. He gave the contract for casting the high quality optical glass blanks, of a size ...
An Achromatic telescope uses an achromatic lens to correct for this. An achromatic lens is a compound lenses made with two types of glass with different dispersion. One element, a concave lens made out of Flint glass, has relatively high dispersion, while the other, a convex element made of Crown glass, has a lower dispersion. The crown lens is ...