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An optical telescope is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct view, or to make a photograph, or to collect data through electronic image sensors. There are three primary types of optical telescope: * refractors, which use lenses (dioptrics) * reflectors, which use mirrors (catoptrics) * catadioptric telescopes, which combine lenses and mirrors A telescope's light gathering power and ability to resolve small detail is directly related to the diameter (or aperture) of its objective (the primary lens or mirror that collects and focuses the light). The larger the objective, the more light the telescope collects and the finer detail it resolves. People use telescopes and binoculars for activities such as observational astronomy, ornithology, pilotage and reconnaissance, and watching sports or performance arts. ==History== The telescope is more a discovery of optical craftsmen than an invention of a scientist.〔(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.” )〕〔(Fred Watson, Stargazer (page 55) )〕 The lens and the properties of refracting and reflecting light had been known since antiquity and theory on how they worked were developed by ancient Greek philosophers, preserved and expanded on in the medieval Islamic world, and had reached a significantly advanced state by the time of the telescope's invention in early modern Europe.〔(The History of the Telescope By Henry C. King, Page 25-29 )〕〔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〕 But the most significant step cited in the invention of the telescope was the development of lens manufacture for spectacles,〔〔(galileo.rice.edu The Galileo Project > Science > The Telescope by Al Van Helden )〕〔(Renaissance Vision from Spectacles to Telescopes By Vincent Ilardi ), page 210〕 first in Venice and Florence in the thirteenth century,〔(galileo.rice.edu The Galileo Project > Science > The Telescope by Al Van Helden '' )〕 and later in the spectacle making centers in both the Netherlands and Germany.〔(The History of the Telescope By Henry C. King, Page 27 "''(spectacles) invention, an important step in the history of the telescope''" )〕 It is in the Netherlands in 1608 where the first recorded optical telescopes (refracting telescopes) appeared. The invention is credited to the spectacle makers Hans Lippershey and Zacharias Janssen in Middelburg, and the instrument-maker and optician Jacob Metius of Alkmaar.〔(galileo.rice.edu The Galileo Project > Science > The Telescope ) by Al Van Helden ''"The Hague discussed the patent applications first of Hans Lipperhey of Middelburg, and then of Jacob Metius of Alkmaar... another citizen of Middelburg, Sacharias Janssen had a telescope at about the same time but was at the Frankfurt Fair where he tried to sell it"''〕 Galileo greatly improved on these designs the following year, and is generally credited as the first to use a telescope for astronomy. Galileo's telescope used Hans Lippershey's design of a convex objective lens and a concave eye lens, and this design is now called a Galilean telescope. Johannes Kepler proposed an improvement on the design〔See his books ''Astronomiae Pars Optica'' and ''Dioptrice''〕 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,〔(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.〕 which corrected the chromatic aberration in Keplerian telescopes up to that time—allowing for much shorter instruments with much larger objectives. For reflecting telescopes, which use a 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.〔(Stargazer - By Fred Watson, Inc NetLibrary, Page 108 )〕 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 as lenses, discussed the idea of building a telescope using a mirror as the image forming objective.〔(Stargazer - By Fred Watson, Inc NetLibrary, Page 109 )〕 The potential advantages of using parabolic mirrors (primarily a reduction of spherical aberration with elimination of chromatic aberration) led to several proposed designs for reflecting telescopes,〔works by Bonaventura Cavalieri and Marin Mersenne among others have designs for reflecting telescopes〕 the most notable of which was published in 1663 by James Gregory and came to be called the Gregorian telescope,〔(Stargazer - By Fred Watson, Inc NetLibrary, Page 117 )〕〔(The History of the Telescope By Henry C. King, Page 71 )〕 but no working models were built. Isaac Newton has been generally credited with constructing the first practical reflecting telescopes, the Newtonian telescope, in 1668〔(Isaac Newton: adventurer in thought, by Alfred Rupert Hall, page 67 )〕 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 mirror fabrication in the 18th century,〔Parabolic mirrors were used much earlier, but James Short perfected their construction. See (【引用サイトリンク】title=Reflecting Telescopes (Newtonian Type) )〕 silver coated glass mirrors in the 19th century, long-lasting aluminum coatings in the 20th century,〔Silvering was introduced by Léon Foucault in 1857, see (madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868) ), and the adoption of long lasting aluminized coatings on reflector mirrors in 1932. (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."'' )〕 segmented mirrors to allow larger diameters, and active optics to compensate for gravitational deformation. A mid-20th century innovation was 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. The late 20th century has seen the development of adaptive optics and space telescopes to overcome the problems of astronomical seeing. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Optical telescope」の詳細全文を読む スポンサード リンク
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