Editing Reflecting telescope (section)

==History==

{{Main|History of the telescope}}

[[File:Newton telescope replica 1668.jpg|thumb|A replica of Newton's second reflecting telescope which was presented to the [[Royal Society]] in 1672.<ref>{{cite book|url=https://books.google.com/books?id=KAWwzHlDVksC&q=history+of+the+telescope |title=The History of the Telescope |author=Henry C. King |page=74 |access-date=2013-08-01|isbn=978-0-486-43265-6 |year=1955 }}</ref>]]
[[Image:Great Telescope, Birr, Offaly 1.jpg|right|thumb|The great telescope of [[Birr Castle]], the [[Leviathan of Parsonstown]]. Modern day remnants of the mirror and support structure.]]

The idea that [[curved mirrors]] behave like lenses dates back at least to [[Alhazen]]'s 11th century treatise on optics, works that had been widely disseminated in Latin translations in [[early modern Europe]].<ref>{{cite book|author=Fred Watson|title=Stargazer: The Life and Times of the Telescope|url=https://books.google.com/books?id=2LZZginzib4C&pg=PA40|year=2007|publisher=Allen & Unwin|isbn=978-1-74176-392-8|page=108}}</ref> Soon after the invention of the [[refracting telescope]], [[Galileo]], [[Giovanni Francesco Sagredo]], and others, spurred on by their knowledge of the principles of curved mirrors, discussed the idea of building a telescope using a mirror as the image forming objective.<ref name="Fred Watson 2007 109">{{cite book|author=Fred Watson|title=Stargazer: The Life and Times of the Telescope|url=https://books.google.com/books?id=2LZZginzib4C&pg=PA40|year=2007|publisher=Allen & Unwin|isbn=978-1-74176-392-8|page=109}}</ref> There were reports that the [[Bologna|Bolognese]] Cesare Caravaggi had constructed one around 1626 and the Italian professor [[Niccolò Zucchi]], in a later work, wrote that he had experimented with a concave bronze mirror in 1616, but said it did not produce a satisfactory image.<ref name="Fred Watson 2007 109"/> The potential advantages of using [[parabolic reflector|parabolic mirrors]], primarily reduction of [[spherical aberration]] with no [[chromatic aberration]], led to many proposed designs for reflecting telescopes. These included one by [[James Gregory (astronomer and mathematician)|James Gregory]], published in 1663. In 1673, experimental scientist [[Robert Hooke]] was able to build this type of telescope, which became known as the [[Gregorian telescope]].<ref>{{cite book|author=Fred Watson|title=Stargazer: The Life and Times of the Telescope|url=https://books.google.com/books?id=2LZZginzib4C&pg=PA62|year=2007|publisher=Allen & Unwin|isbn=978-1-74176-392-8|page=117}}</ref><ref name=":0">{{cite book |author=Henry C. King |url=https://archive.org/details/historyoftelesco0000henr/page/71 |title=The History of the Telescope |publisher=Richard Griffin & Co |year=1955 |isbn=978-0-486-43265-6 |page=68–72}}</ref><ref>{{Cite web|url=http://www.nms.ac.uk/explore/stories/science-and-technology/reflecting-telescope/telescopes/james-gregory/|title=Explore, National Museums Scotland|access-date=2016-11-15|archive-date=2017-01-17|archive-url=https://web.archive.org/web/20170117064000/http://www.nms.ac.uk/explore/stories/science-and-technology/reflecting-telescope/telescopes/james-gregory/|url-status=dead}}</ref>

Five years after Gregory designed his telescope and five years before Hooke built the first such Gregorian telescope, [[Isaac Newton]] in 1668 built [[Newton's reflector|his own reflecting telescope]], which is considered the first reflecting telescope.<ref name=":0" /><ref name="books.google.com">{{cite book |author=A. Rupert Hall |url=https://archive.org/details/isaacnewtonadven0000hall/page/67 |title=Isaac Newton: Adventurer in Thought |publisher=Cambridge University Press |year=1996 |isbn=978-0-521-56669-8 |page=67–68 |url-access=registration}}</ref><ref name=":172">{{Cite book |last=Rowlands |first=Peter |url=https://books.google.com/books?id=ipA4DwAAQBAJ&pg=PA245 |title=Newton and the Great World System |date=2017 |publisher=[[World Scientific Publishing]] |isbn=978-1-78634-372-7 |pages=245 |language=en |doi=10.1142/q0108}}</ref> It used a spherically ground metal [[primary mirror]] and a small diagonal mirror in an optical configuration that has come to be known as the [[Newtonian telescope]].

Despite the theoretical advantages of the reflector design, the difficulty of construction and the poor performance of the [[speculum metal]] mirrors being used at the time meant it took over 100 years for them to become popular. Many of the advances in reflecting telescopes included the perfection of [[parabolic reflector|parabolic mirror]] fabrication in the 18th century,<ref>Parabolic mirrors were used much earlier, but [[James Short (mathematician)|James Short]] perfected their construction. See {{cite web |url=http://www.astro.lsa.umich.edu/undergrad/Labs/optics/Reflectors.html |title=Reflecting Telescopes (Newtonian Type) |publisher=Astronomy Department, University of Michigan |url-status=dead |archive-url=https://web.archive.org/web/20090131173814/http://www.astro.lsa.umich.edu/undergrad/Labs/optics/Reflectors.html |archive-date=2009-01-31 }}</ref> silver coated glass mirrors in the 19th century (built by [[Léon Foucault]] in 1858),<ref>{{Cite journal|last=Lequeux|first=James|date=2017-01-01|title=The Paris Observatory has 350 years|url=https://ui.adsabs.harvard.edu/abs/2017LAstr.131a..28L|journal=L'Astronomie|volume=131|pages=28–37|bibcode=2017LAstr.131a..28L|issn=0004-6302}}</ref> long-lasting aluminum coatings in the 20th century,<ref>Silvering on a reflecting telescope was introduced by [[Léon Foucault]] in 1857, see [http://www.madehow.com/inventorbios/39/Jean-Bernard-L-on-Foucault.html  madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819–1868)], and the adoption of long lasting aluminized coatings on reflector mirrors in 1932. [http://www.cambridge.org/uk/astronomy/features/amateur/files/p28-4.pdf Bakich sample pages Chapter 2, Page 3 ''"John Donavan Strong, a young physicist at the California Institute of Technology, was one of the first to coat a mirror with aluminum. He did it by thermal vacuum evaporation. The first mirror he aluminized, in 1932, is the earliest known example of a telescope mirror coated by this technique."'']</ref> [[segmented mirror]]s to allow larger diameters, and [[active optics]] to compensate for gravitational deformation. A mid-20th century innovation was [[catadioptric system|catadioptric]] telescopes such as the [[Schmidt camera]], which use both a spherical mirror and a lens (called a corrector plate) as primary optical elements, mainly used for wide-field imaging without spherical aberration.

The late 20th century has seen the development of [[adaptive optics]] and [[lucky imaging]] to overcome the problems of [[astronomical seeing|seeing]], and reflecting telescopes are ubiquitous on [[space telescope]]s and many types of [[spacecraft]] imaging devices.