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Another type is the high-reflector coating, which can be used to produce mirrors that reflect greater than 99.99% of the light that falls on them. More complex optical coatings exhibit high reflection over some range of wavelengths , and anti-reflection over another range, allowing the production of dichroic thin-film filters .
An aluminum vacuum-deposition process invented in 1930 by Caltech physicist and astronomer John Strong, led to most reflecting telescopes shifting to aluminum. [11] Nevertheless, some modern telescopes use silver, such as the Kepler Space Telescope. The Kepler mirror's silver was deposited using ion assisted evaporation. [12] [13]
The primary mirror in most modern telescopes is composed of a solid glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is vacuum deposited onto the mirror, forming a highly reflective first surface mirror. Some telescopes use primary mirrors which are made differently.
John D. Strong used evaporation coating to make the first aluminium-coated telescope mirrors in the 1930s. [28] The first dielectric mirror was created in 1937 by Auwarter using evaporated rhodium. [17] The metal coating of glass mirrors is usually protected from abrasion and corrosion by a layer of paint applied over it.
Telescopes with speculum metal mirrors were a large breakthrough in aperture, but their drawbacks fueled competition from refractors The metal mirror of the Leviathan, the largest telescope mirror until the 100-inch Hooker telescope of 1917 (a metal-on-glass mirror) Looking down the insides of an old reflecting telescope. It's not clear whether ...
Objective: The first lens or curved mirror that collects and focuses the incoming light. 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.
The Keck II Telescope showing the segmented primary mirror made of Zerodur. The main applications for Zerodur include telescope optics in astronomy [2] and space applications, [3] lithography machines for microchips and displays, [4] and inertial measurements systems for navigation.
Silvering was put on the mirror chemically, typically by the mirror maker or user. Silver coatings have higher reflectivity than aluminum but corrode quickly and need replacing after a few months. Since the 1950s most mirror makers have an aluminum coating applied by a thin-film deposition process (work is done by a firm specializing in the ...