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Zerodur has both an amorphous (vitreous) component and a crystalline component. Its most important properties [21] are: . The material exhibits a particularly low thermal expansion, with a mean value of 0 ± 0.007×10 −6 K −1 within the temperature range of 0 to 50 °C.
The era of the large glass-mirror reflector had begun, with telescopes such as Andrew Ainslie Common's 1879 36-inch (91 cm) and 1887 60-inch (152 cm) reflectors built at Ealing, and the first of the "modern" large glass-mirror research reflectors, 60-inch (150 cm) Mount Wilson Observatory Hale Telescope of 1908, the 100-inch (2.5 m) Mount ...
Optically coated mirrors and lenses. An optical coating is one or more thin layers of material deposited on an optical component such as a lens, prism or mirror, which alters the way in which the optic reflects and transmits light. These coatings have become a key technology in the field of optics.
Bokeh of a mirror lens, with ring pattern in out of focus areas. Several companies made catadioptric lenses throughout the later part of the 20th century. Nikon (under the Mirror- Nikkor and later Reflex- Nikkor names) and Canon both offered several designs, such as 500 mm 1:8 and 1000 mm 1:11.
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The mercury mirror of the Large Zenith Telescope in Canada was the largest liquid-metal mirror ever built. It had a diameter of 6 meters and rotated at a rate of about 8.5 revolutions per minute. It was decommissioned in 2016. [4] This mirror was a test, built for $1 million, but it was not suitable for astronomy because of the test site's weather.
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Adaptive thin shell mirror. [5]Adaptive optics was first envisioned by Horace W. Babcock in 1953, [6] [7] and was also considered in science fiction, as in Poul Anderson's novel Tau Zero (1970), but it did not come into common usage until advances in computer technology during the 1990s made the technique practical.