Editing Optical telescope (section)

==History==
{{Further|History of the telescope}}

The telescope is more a discovery of optical craftsmen than an invention of a scientist.<ref>[http://galileo.rice.edu/sci/instruments/telescope.html galileo.rice.edu '''The Galileo Project > Science > The Telescope''' by Al Van Helden – "the telescope was not the invention of scientists; rather, it was the product of craftsmen."]</ref><ref name="LZZginzib4C page 55">{{cite book|author=Fred Watson|title=Ian 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=55}}</ref> The [[Lens (optics)|lens]] and the properties of refracting and reflecting light had been known since [[Ancient history|antiquity]], and theory on how they worked was developed by ancient [[Greek philosophy|Greek]] philosophers, preserved and expanded on in the [[Islamic Golden Age|medieval Islamic world]], and had reached a significantly advanced state by the time of the telescope's invention in [[early modern Europe]].<ref>{{cite book|author=Henry C. King|title=The History of the Telescope|url=https://books.google.com/books?id=KAWwzHlDVksC&pg=PR1|year=2003|publisher=Courier Corporation|isbn=978-0-486-43265-6|pages=25–29}}</ref><ref>progression is followed through [[Robert Grosseteste]] [[Witelo]], [[Roger Bacon]], through [[Johannes Kepler]], D. C. Lindberg, Theories of Vision from al-Kindi to Kepler, (Chicago: Univ. of Chicago Pr., 1976), pp. 94–99</ref> But the most significant step cited in the invention of the telescope was the development of lens manufacture for [[Glasses|spectacles]],<ref name="LZZginzib4C page 55"/><ref name="galileo.rice.edu">[http://galileo.rice.edu/sci/instruments/telescope.html galileo.rice.edu '''The Galileo Project > Science > The Telescope''' by Al Van Helden]</ref><ref>[https://books.google.com/books?id=peIL7hVQUmwC&pg=PA218&dq=invention+of+the+telescope&lr=#PPA26,M1 '''Renaissance Vision from Spectacles to Telescopes''' By Vincent Ilardi], page 210</ref> first in Venice and Florence in the thirteenth century,<ref name="galileo.rice.edu"/> and later in the spectacle making centers in both the [[Netherlands]] and Germany.<ref>{{cite book|author=Henry C. King|title=The History of the Telescope|url=https://books.google.com/books?id=KAWwzHlDVksC&pg=PR1|year=2003|publisher=Courier Corporation|isbn=978-0-486-43265-6|page=27|quote="(spectacles) invention, an important step in the history of the telescope"}}</ref> It is in the Netherlands in 1608 where the first documents describing a [[refracting telescope|refracting optical telescope]] surfaced in the form of a patent filed by spectacle maker [[Hans Lippershey]], followed a few weeks later by claims by [[Jacob Metius]], and a third unknown applicant, that they also knew of this "art".<ref>Albert Van Helden, Sven Dupré, Rob van Gent, The Origins of the Telescope, Amsterdam University Press, 2010, pages 3-4, 15</ref>

Word of the invention spread fast and [[Galileo Galilei]], on hearing of the device, was making his own improved designs within a year and was the first to publish astronomical results using a telescope.<ref>Albert Van Helden, Sven Dupré, Rob van Gent, The Origins of the Telescope, Amsterdam University Press, 2010, page 183</ref> Galileo's telescope used a convex [[Objective (optics)|objective lens]] and a concave [[Eyepiece|eye lens]], a design is now called a [[Galilean telescope]]. [[Johannes Kepler]] proposed an improvement on the design<ref>See his books ''[[Johannes Kepler#Prague (1600–1612)|Astronomiae Pars Optica]]'' and ''[[Johannes Kepler#Prague (1600–1612)|Dioptrice]]''</ref> that used a convex [[eyepiece]], often called the [[Keplerian Telescope]].

The next big step in the development of refractors was the advent of the [[Achromatic lens]] in the early 18th century,<ref>[http://www.mhs.ox.ac.uk/sphaera/index.htm?issue8/articl5 Sphaera - Peter Dollond answers Jesse Ramsden] - A review of the events of the invention of the achromatic doublet with emphasis on the roles of Hall, Bass, John Dollond and others.</ref> which corrected the [[chromatic aberration]] in Keplerian telescopes up to that time, allowing for much shorter instruments with much larger objectives.{{citation needed|date=February 2021}} [[Chester Moore Hall|Chester Moor Hall]] is credited with designing the first achromatic lens in 1729, which consisted of a concave [[Crown glass (optics)|crown]] and a convex [[Flint glass|flint]] lens. However, it was [[John Dollond]] who received the first patent after further development of the design.<ref>{{Cite journal |last=King |first=H. C. |date=1948 |title=The invention and early development of the achromatic telescope |url=https://adsabs.harvard.edu/full/1948PA.....56...75K |journal=Popular Astronomy |volume=56 |pages=75}}</ref>

For [[reflecting telescope]]s, which use a [[curved mirrors|curved mirror]] in place of the objective lens, theory preceded practice. The theoretical basis for [[curved mirrors]] behaving similar to lenses was probably established by [[Alhazen]], whose theories had been widely disseminated in Latin translations of his work.<ref>{{cite book|author=Fred Watson|title=Ian 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 that curved mirrors had similar properties to lenses, discussed the idea of building a telescope using a mirror as the image forming objective.<ref>{{cite book|author=Fred Watson|title=Ian 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> The potential advantages of using [[parabolic reflector|parabolic mirrors]] (primarily a reduction of [[spherical aberration]] with elimination of [[chromatic aberration]]) led to several proposed designs for reflecting telescopes,<ref>works by [[Bonaventura Cavalieri]] and [[Marin Mersenne]] among others have designs for reflecting telescopes</ref> the most notable of which was published in 1663 by [[James Gregory (astronomer and mathematician)|James Gregory]] and came to be called the [[Gregorian telescope]],<ref>{{cite book|author=Fred Watson|title=Ian 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=117}}</ref><ref>{{cite book|author=Henry C. King|title=The History of the Telescope|url=https://books.google.com/books?id=KAWwzHlDVksC&pg=PR1|year=2003|publisher=Courier Corporation|isbn=978-0-486-43265-6|page=71}}</ref> but no working models were built. [[Isaac Newton]] has been generally credited with constructing the first practical reflecting telescopes, the [[Newtonian telescope]], in 1668<ref name="books.google.com">{{cite book|author=A. Rupert Hall|title=Isaac Newton: Adventurer in Thought|url=https://archive.org/details/isaacnewtonadven0000hall|url-access=registration|year=1996|publisher=Cambridge University Press|isbn=978-0-521-56669-8|page=[https://archive.org/details/isaacnewtonadven0000hall/page/67 67]}}</ref> although due to their difficulty of construction and the poor performance of the [[speculum metal]] mirrors used it took over 100 years for reflectors 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}}</ref> silver coated glass mirrors in the 19th century, long-lasting aluminum coatings in the 20th century,<ref>Silvering 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 uses both a lens (corrector plate) and mirror as primary optical elements, mainly used for wide field imaging without spherical aberration.{{citation needed|date=February 2021}}

The late 20th century has seen the development of [[adaptive optics]] and [[space telescope]]s to overcome the problems of [[astronomical seeing]].{{citation needed|date=February 2021}}

The electronics revolution of the early 21st century led to the development of computer-connected telescopes in the 2010s that allow non-professional skywatchers to observe stars and satellites using relatively low-cost equipment by taking advantage of [[digital photography|digital]] [[astrophotography|astrophotographic]] techniques developed by professional astronomers over previous decades. An electronic connection to a computer ([[smartphone]], [[Tablet computer|pad]], or laptop) is [[Afocal photography|required to make astronomical observations]] from the telescopes. The digital technology allows [[Dark-frame subtraction|multiple images to be stacked while subtracting the noise component of the observation]] producing images of [[Messier objects]] and [[Star#Magnitude|faint stars]] as dim as an [[apparent magnitude]] of 15 with consumer-grade equipment.<ref name=ciel201811>{{cite news |url=https://www.cieletespace.fr/actualites/les-telescopes-connectes-debarquent-episode-2-2-l-evscope |title=Les télescopes connectés débarquent. Episode 2/2 : l'eVscope |language=French |trans-title=The connected telescopes land. Episode 2/2: the eVscope |work=Ciel & espace |publisher=L'Association Française d'Astronomie |date=November 2018 |accessdate=29 June 2019 |archive-url=https://web.archive.org/web/20190629153752/https://www.cieletespace.fr/actualites/les-telescopes-connectes-debarquent-episode-2-2-l-evscope |archive-date=29 June 2019 |url-status=live }}</ref><ref name=sa20171010>{{cite news |last=Billings |first=Lee |url=https://blogs.scientificamerican.com/observations/new-telescope-gives-back-the-sky-to-city-dwellers/ |title=New Telescope 'Gives Back the Sky' to City-Dwellers |work=[[Scientific American]] |date=13 September 2018 |accessdate=29 June 2019 |archive-url=https://web.archive.org/web/20190327183819/https://blogs.scientificamerican.com/observations/new-telescope-gives-back-the-sky-to-city-dwellers/ |archive-date=27 March 2019 |url-status=live }}</ref><!-- examples include the Stellina by Vaonis<ref name=sdc20190629>[https://www.space.com/stellina-smart-telescope-review.html Stellina Smart Telescope Makes Astrophotography a Breeze] {{Webarchive|url=https://web.archive.org/web/20191010010232/https://www.space.com/stellina-smart-telescope-review.html |date=10 October 2019 }}, [[space.com]], 2 October 2019, accessed 10 October 2019.</ref> and the eVscope by [[Unistellar]]<ref name=ciel201811/> -->