The following is a list of the largest optical reflecting telescopes sorted by mirror diameter. Note that two of the first three are not yet operational. This list does not currently include telescopes that are still in the conceptual/proposed stage, such as the Overwhelmingly Large Telescope or the European Extremely Large Telescope; the design stage, such as the Thirty Meter Telescope; or ones still in the early stages of manufacturing such as the Giant Magellan Telescope.
The Hobby-Eberly Telescope is a 9.2 meter telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs.
A refracting or refractor telescope is a dioptric telescope that uses a lens as its objective to form an image. The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used in other devices such as binoculars and long or telephoto camera lenses.
The Large Binocular Telescope (LBT, originally named the Columbus Project) is located on 10,700-foot Mount Graham in the Pinaleno Mountains of southeastern Arizona and is a part of the Mount Graham International Observatory. As of 2008[update], the LBT is the world's highest resolution and most technologically advanced optical telescope, creating images in the near-infrared with 10 times the resolution of the Hubble Space Telescope
The William Herschel Telescope or WHT was first conceived in the late 1960s, when the Anglo-Australian Observatory was being designed. The British astronomical community saw the need for telescopes of comparable power in the Northern Hemisphere. Planning began in 1974, but by 1979 the project was on the verge of being scrapped due to a ballooning budget. A re-design cut the price-tag substantially, and Dutch astronomers took a 20% stake in the project, allowing the project to be given the go-ahead in 1981. That year was the 200th anniversary of the discovery of Uranus by William Herschel, and it was decided to name the telescope in his honour. The telescope is a member of the Isaac Newton Group of Telescopes.