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class="vector-toc-numb">3</span> <span>Use in astronomical research</span> </div> </a> <ul id="toc-Use_in_astronomical_research-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Reflecting_telescope_designs" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Reflecting_telescope_designs"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Reflecting telescope designs</span> </div> </a> <button aria-controls="toc-Reflecting_telescope_designs-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Reflecting telescope designs subsection</span> </button> <ul id="toc-Reflecting_telescope_designs-sublist" class="vector-toc-list"> <li id="toc-Gregorian" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Gregorian"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>Gregorian</span> </div> </a> <ul id="toc-Gregorian-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Newtonian" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Newtonian"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>Newtonian</span> </div> </a> <ul id="toc-Newtonian-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-The_Cassegrain_design_and_its_variations" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#The_Cassegrain_design_and_its_variations"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3</span> <span>The Cassegrain design and its variations</span> </div> </a> <ul id="toc-The_Cassegrain_design_and_its_variations-sublist" class="vector-toc-list"> <li id="toc-Ritchey–Chrétien" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Ritchey–Chrétien"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3.1</span> <span>Ritchey–Chrétien</span> </div> </a> <ul id="toc-Ritchey–Chrétien-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Three-mirror_anastigmat" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Three-mirror_anastigmat"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3.2</span> <span>Three-mirror anastigmat</span> </div> </a> <ul id="toc-Three-mirror_anastigmat-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Dall–Kirkham" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Dall–Kirkham"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3.3</span> <span>Dall–Kirkham</span> </div> </a> <ul id="toc-Dall–Kirkham-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Off-axis_designs" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Off-axis_designs"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4</span> <span>Off-axis designs</span> </div> </a> <ul id="toc-Off-axis_designs-sublist" class="vector-toc-list"> <li id="toc-Herschelian" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Herschelian"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4.1</span> <span>Herschelian</span> </div> </a> <ul id="toc-Herschelian-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Schiefspiegler" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Schiefspiegler"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4.2</span> <span>Schiefspiegler</span> </div> </a> <ul id="toc-Schiefspiegler-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Stevick-Paul" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Stevick-Paul"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4.3</span> <span>Stevick-Paul</span> </div> </a> <ul id="toc-Stevick-Paul-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Yolo" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Yolo"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4.4</span> <span>Yolo</span> </div> </a> <ul id="toc-Yolo-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Liquid-mirror_telescopes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Liquid-mirror_telescopes"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.5</span> <span>Liquid-mirror telescopes</span> </div> </a> <ul id="toc-Liquid-mirror_telescopes-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Focal_planes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Focal_planes"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Focal planes</span> </div> </a> <button aria-controls="toc-Focal_planes-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Focal planes subsection</span> </button> <ul id="toc-Focal_planes-sublist" class="vector-toc-list"> <li id="toc-Prime_focus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Prime_focus"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1</span> <span>Prime focus</span> </div> </a> <ul id="toc-Prime_focus-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Cassegrain_focus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Cassegrain_focus"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.2</span> <span>Cassegrain focus</span> </div> </a> <ul id="toc-Cassegrain_focus-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Nasmyth_and_coudé_focus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Nasmyth_and_coudé_focus"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.3</span> <span>Nasmyth and coudé focus</span> </div> </a> <ul id="toc-Nasmyth_and_coudé_focus-sublist" class="vector-toc-list"> <li id="toc-Nasmyth" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Nasmyth"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.3.1</span> <span>Nasmyth</span> </div> </a> <ul id="toc-Nasmyth-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Coudé" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Coudé"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.3.2</span> <span>Coudé</span> </div> </a> <ul id="toc-Coudé-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Fibre-fed_spectrographs" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Fibre-fed_spectrographs"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.4</span> <span>Fibre-fed spectrographs</span> </div> </a> <ul id="toc-Fibre-fed_spectrographs-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Reflecting telescope</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 42 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-42" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">42 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D9%85%D9%82%D8%B1%D8%A7%D8%A8_%D8%B9%D8%A7%D9%83%D8%B3" title="مقراب عاكس – Arabic" lang="ar" hreflang="ar" data-title="مقراب عاكس" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/Telescopiu_reflector" title="Telescopiu reflector – Asturian" lang="ast" hreflang="ast" data-title="Telescopiu reflector" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Reflektor_(teleskop)" title="Reflektor (teleskop) – Azerbaijani" lang="az" hreflang="az" data-title="Reflektor (teleskop)" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%AA%E0%A7%8D%E0%A6%B0%E0%A6%A4%E0%A6%BF%E0%A6%AB%E0%A6%B2%E0%A6%95_%E0%A6%A6%E0%A7%82%E0%A6%B0%E0%A6%AC%E0%A7%80%E0%A6%95%E0%A7%8D%E0%A6%B7%E0%A6%A3_%E0%A6%AF%E0%A6%A8%E0%A7%8D%E0%A6%A4%E0%A7%8D%E0%A6%B0" title="প্রতিফলক দূরবীক্ষণ যন্ত্র – Bangla" lang="bn" hreflang="bn" data-title="প্রতিফলক দূরবীক্ষণ যন্ত্র" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%A0%D0%B5%D1%84%D0%BB%D0%B5%D0%BA%D1%82%D0%BE%D1%80%D0%B5%D0%BD_%D1%82%D0%B5%D0%BB%D0%B5%D1%81%D0%BA%D0%BE%D0%BF" title="Рефлекторен телескоп – Bulgarian" lang="bg" hreflang="bg" data-title="Рефлекторен телескоп" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Telescopi_reflector" title="Telescopi reflector – Catalan" lang="ca" hreflang="ca" data-title="Telescopi reflector" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Spejlteleskop" title="Spejlteleskop – Danish" lang="da" hreflang="da" data-title="Spejlteleskop" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Spiegelteleskop" title="Spiegelteleskop – German" lang="de" hreflang="de" data-title="Spiegelteleskop" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%9A%CE%B1%CF%84%CE%BF%CF%80%CF%84%CF%81%CE%B9%CE%BA%CF%8C_%CF%84%CE%B7%CE%BB%CE%B5%CF%83%CE%BA%CF%8C%CF%80%CE%B9%CE%BF" title="Κατοπτρικό τηλεσκόπιο – Greek" lang="el" hreflang="el" data-title="Κατοπτρικό τηλεσκόπιο" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Telescopio_reflector" title="Telescopio reflector – Spanish" lang="es" hreflang="es" data-title="Telescopio reflector" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Islatze-teleskopio" title="Islatze-teleskopio – Basque" lang="eu" hreflang="eu" data-title="Islatze-teleskopio" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%AA%D9%84%D8%B3%DA%A9%D9%88%D9%BE_%D8%A8%D8%A7%D8%B2%D8%AA%D8%A7%D8%A8%DB%8C" title="تلسکوپ بازتابی – Persian" lang="fa" hreflang="fa" data-title="تلسکوپ بازتابی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr badge-Q70894304 mw-list-item" title=""><a href="https://fr.wikipedia.org/wiki/T%C3%A9lescope_r%C3%A9flecteur" title="Télescope réflecteur – French" lang="fr" hreflang="fr" data-title="Télescope réflecteur" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Telescopio_reflector" title="Telescopio reflector – Galician" lang="gl" hreflang="gl" data-title="Telescopio reflector" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EB%B0%98%EC%82%AC_%EB%A7%9D%EC%9B%90%EA%B2%BD" title="반사 망원경 – Korean" lang="ko" hreflang="ko" data-title="반사 망원경" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D5%8C%D5%A5%D6%86%D5%AC%D5%A5%D5%AF%D5%BF%D5%B8%D6%80" title="Ռեֆլեկտոր – Armenian" lang="hy" hreflang="hy" data-title="Ռեֆլեկտոր" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%AA%E0%A4%B0%E0%A4%BE%E0%A4%B5%E0%A4%B0%E0%A5%8D%E0%A4%A4%E0%A5%80_%E0%A4%A6%E0%A5%82%E0%A4%B0%E0%A4%A6%E0%A4%B0%E0%A5%8D%E0%A4%B6%E0%A5%80" title="परावर्ती दूरदर्शी – Hindi" lang="hi" hreflang="hi" data-title="परावर्ती दूरदर्शी" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Reflektorski_teleskop" title="Reflektorski teleskop – Croatian" lang="hr" hreflang="hr" data-title="Reflektorski teleskop" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Teleskop_pemantul" title="Teleskop pemantul – Indonesian" lang="id" hreflang="id" data-title="Teleskop pemantul" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Telescopio_riflettore" title="Telescopio riflettore – Italian" lang="it" hreflang="it" data-title="Telescopio riflettore" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%98%D7%9C%D7%A1%D7%A7%D7%95%D7%A4_%D7%9E%D7%97%D7%96%D7%99%D7%A8_%D7%90%D7%95%D7%A8" title="טלסקופ מחזיר אור – Hebrew" lang="he" hreflang="he" data-title="טלסקופ מחזיר אור" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%A0%D0%B5%D1%84%D0%BB%D0%B5%D0%BA%D1%82%D0%BE%D1%80_(%D1%82%D0%B5%D0%BB%D0%B5%D1%81%D0%BA%D0%BE%D0%BF)" title="Рефлектор (телескоп) – Kazakh" lang="kk" hreflang="kk" data-title="Рефлектор (телескоп)" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-ht mw-list-item"><a href="https://ht.wikipedia.org/wiki/Telesk%C3%B2p_reflekt%C3%A8" title="Teleskòp reflektè – Haitian Creole" lang="ht" hreflang="ht" data-title="Teleskòp reflektè" data-language-autonym="Kreyòl ayisyen" data-language-local-name="Haitian Creole" class="interlanguage-link-target"><span>Kreyòl ayisyen</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Reflektors" title="Reflektors – Latvian" lang="lv" hreflang="lv" data-title="Reflektors" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Reflektorius" title="Reflektorius – Lithuanian" lang="lt" hreflang="lt" data-title="Reflektorius" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%A0%D0%B5%D1%84%D0%BB%D0%B5%D0%BA%D1%82%D0%BE%D1%80%D1%81%D0%BA%D0%B8_%D1%82%D0%B5%D0%BB%D0%B5%D1%81%D0%BA%D0%BE%D0%BF" title="Рефлекторски телескоп – Macedonian" lang="mk" hreflang="mk" data-title="Рефлекторски телескоп" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Spiegeltelescoop" title="Spiegeltelescoop – Dutch" lang="nl" hreflang="nl" data-title="Spiegeltelescoop" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E5%8F%8D%E5%B0%84%E6%9C%9B%E9%81%A0%E9%8F%A1" title="反射望遠鏡 – Japanese" lang="ja" hreflang="ja" data-title="反射望遠鏡" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Reflektorteleskop" title="Reflektorteleskop – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Reflektorteleskop" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Reflektor_i_astronomi" title="Reflektor i astronomi – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Reflektor i astronomi" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Teleskop_zwierciadlany" title="Teleskop zwierciadlany – Polish" lang="pl" hreflang="pl" data-title="Teleskop zwierciadlany" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Telesc%C3%B3pio_refletor" title="Telescópio refletor – Portuguese" lang="pt" hreflang="pt" data-title="Telescópio refletor" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%A0%D0%B5%D1%84%D0%BB%D0%B5%D0%BA%D1%82%D0%BE%D1%80_(%D1%82%D0%B5%D0%BB%D0%B5%D1%81%D0%BA%D0%BE%D0%BF)" title="Рефлектор (телескоп) – Russian" lang="ru" hreflang="ru" data-title="Рефлектор (телескоп)" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Reflektor_(astron%C3%B3mia)" title="Reflektor (astronómia) – Slovak" lang="sk" hreflang="sk" data-title="Reflektor (astronómia)" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%A0%D0%B5%D1%84%D0%BB%D0%B5%D0%BA%D1%82%D0%BE%D1%80_(%D1%82%D0%B5%D0%BB%D0%B5%D1%81%D0%BA%D0%BE%D0%BF)" title="Рефлектор (телескоп) – Serbian" lang="sr" hreflang="sr" data-title="Рефлектор (телескоп)" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%A4%E0%AF%86%E0%AE%B1%E0%AE%BF%E0%AE%AA%E0%AF%8D%E0%AE%AA%E0%AF%81%E0%AE%B5%E0%AE%95%E0%AF%88%E0%AE%A4%E0%AF%8D_%E0%AE%A4%E0%AF%8A%E0%AE%B2%E0%AF%88%E0%AE%A8%E0%AF%8B%E0%AE%95%E0%AF%8D%E0%AE%95%E0%AE%BF" title="தெறிப்புவகைத் தொலைநோக்கி – Tamil" lang="ta" hreflang="ta" data-title="தெறிப்புவகைத் தொலைநோக்கி" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%81%E0%B8%A5%E0%B9%89%E0%B8%AD%E0%B8%87%E0%B9%82%E0%B8%97%E0%B8%A3%E0%B8%97%E0%B8%A3%E0%B8%A3%E0%B8%A8%E0%B8%99%E0%B9%8C%E0%B8%AA%E0%B8%B0%E0%B8%97%E0%B9%89%E0%B8%AD%E0%B8%99%E0%B9%81%E0%B8%AA%E0%B8%87" title="กล้องโทรทรรศน์สะท้อนแสง – Thai" lang="th" hreflang="th" data-title="กล้องโทรทรรศน์สะท้อนแสง" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Yans%C4%B1tmal%C4%B1_teleskop" title="Yansıtmalı teleskop – Turkish" lang="tr" hreflang="tr" data-title="Yansıtmalı teleskop" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%A0%D0%B5%D1%84%D0%BB%D0%B5%D0%BA%D1%82%D0%BE%D1%80_(%D1%82%D0%B5%D0%BB%D0%B5%D1%81%D0%BA%D0%BE%D0%BF)" title="Рефлектор (телескоп) – Ukrainian" lang="uk" hreflang="uk" data-title="Рефлектор (телескоп)" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/K%C3%ADnh_vi%E1%BB%85n_v%E1%BB%8Dng_ph%E1%BA%A3n_x%E1%BA%A1" title="Kính viễn vọng phản xạ – Vietnamese" lang="vi" hreflang="vi" data-title="Kính viễn vọng phản xạ" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E5%8F%8D%E5%B0%84%E6%9C%9B%E9%81%A0%E9%8F%A1" title="反射望遠鏡 – Cantonese" lang="yue" hreflang="yue" data-title="反射望遠鏡" data-language-autonym="粵語" data-language-local-name="Cantonese" class="interlanguage-link-target"><span>粵語</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E5%8F%8D%E5%B0%84%E6%9C%9B%E8%BF%9C%E9%95%9C" title="反射望远镜 – Chinese" lang="zh" hreflang="zh" data-title="反射望远镜" data-language-autonym="中文" data-language-local-name="Chinese" 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id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Telescopes which utilize curved mirrors to form an image</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:SOFIA_2.5M_Primary_Mirror.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ee/SOFIA_2.5M_Primary_Mirror.jpg/220px-SOFIA_2.5M_Primary_Mirror.jpg" decoding="async" width="220" height="161" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ee/SOFIA_2.5M_Primary_Mirror.jpg/330px-SOFIA_2.5M_Primary_Mirror.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ee/SOFIA_2.5M_Primary_Mirror.jpg/440px-SOFIA_2.5M_Primary_Mirror.jpg 2x" data-file-width="5219" data-file-height="3827" /></a><figcaption><a href="/wiki/Stratospheric_Observatory_for_Infrared_Astronomy" title="Stratospheric Observatory for Infrared Astronomy">Stratospheric Observatory for Infrared Astronomy</a> </figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Franklin_reflector_24.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Franklin_reflector_24.jpg/220px-Franklin_reflector_24.jpg" decoding="async" width="220" height="170" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Franklin_reflector_24.jpg/330px-Franklin_reflector_24.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Franklin_reflector_24.jpg/440px-Franklin_reflector_24.jpg 2x" data-file-width="900" data-file-height="696" /></a><figcaption>24-inch convertible Newtonian/Cassegrain reflecting telescope on display at the <a href="/wiki/Franklin_Institute" title="Franklin Institute">Franklin Institute</a></figcaption></figure> <p>A <b>reflecting telescope</b> (also called a <b>reflector</b>) is a <a href="/wiki/Telescope" title="Telescope">telescope</a> that uses a single or a combination of <a href="/wiki/Curved_mirror" title="Curved mirror">curved mirrors</a> that reflect <a href="/wiki/Light" title="Light">light</a> and form an <a href="/wiki/Image" title="Image">image</a>. The reflecting telescope was invented in the 17th century by <a href="/wiki/Isaac_Newton" title="Isaac Newton">Isaac Newton</a> as an alternative to the <a href="/wiki/Refracting_telescope" title="Refracting telescope">refracting telescope</a> which, at that time, was a design that suffered from severe <a href="/wiki/Chromatic_aberration" title="Chromatic aberration">chromatic aberration</a>. Although reflecting telescopes produce other types of <a href="/wiki/Optical_aberration" title="Optical aberration">optical aberrations</a>, it is a design that allows for very large diameter <a href="/wiki/Objective_(optics)" title="Objective (optics)">objectives</a>. Almost all of the major telescopes used in <a href="/wiki/Astronomy" title="Astronomy">astronomy</a> research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use <a href="/wiki/Mirror" title="Mirror">mirrors</a>, the design is sometimes referred to as a <b><a href="/wiki/Catoptrics" title="Catoptrics">catoptric</a> telescope</b>. </p><p>From the time of Newton to the 1800s, the mirror itself was made of metal – usually <a href="/wiki/Speculum_metal" title="Speculum metal">speculum metal</a>. This type included Newton's first designs and the largest telescope of the 19th century, the <a href="/wiki/Leviathan_of_Parsonstown" title="Leviathan of Parsonstown">Leviathan of Parsonstown</a> with a 6 feet (1.8 m) wide metal mirror. In the 19th century a new method using a block of glass coated with very thin layer of silver began to become more popular by the turn of the century. Common telescopes which led to the <a href="/wiki/Crossley_telescope" title="Crossley telescope">Crossley</a> and Harvard reflecting telescopes, which helped establish a better reputation for reflecting telescopes as the metal mirror designs were noted for their drawbacks. Chiefly the metal mirrors only reflected about <style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span> of the light and the metal would <a href="/wiki/Tarnish" title="Tarnish">tarnish</a>. After multiple polishings and tarnishings, the mirror could lose its precise figuring needed. </p><p>Reflecting telescopes became extraordinarily popular for astronomy and many famous telescopes, such as the <a href="/wiki/Hubble_Space_Telescope" title="Hubble Space Telescope">Hubble Space Telescope</a>, and popular amateur models use this design. In addition, the reflection telescope principle was applied to other electromagnetic wavelengths, and for example, <a href="/wiki/X-ray_telescope" title="X-ray telescope">X-ray telescopes</a> also use the reflection principle to make <a href="/wiki/Image-forming_optical_system" title="Image-forming optical system">image-forming optics</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/History_of_the_telescope" title="History of the telescope">History of the telescope</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Newton_telescope_replica_1668.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/db/Newton_telescope_replica_1668.jpg/220px-Newton_telescope_replica_1668.jpg" decoding="async" width="220" height="282" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/db/Newton_telescope_replica_1668.jpg/330px-Newton_telescope_replica_1668.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/db/Newton_telescope_replica_1668.jpg/440px-Newton_telescope_replica_1668.jpg 2x" data-file-width="1134" data-file-height="1452" /></a><figcaption>A replica of Newton's second reflecting telescope which was presented to the <a href="/wiki/Royal_Society" title="Royal Society">Royal Society</a> in 1672.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></figcaption></figure> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Great_Telescope,_Birr,_Offaly_1.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/en/thumb/f/fe/Great_Telescope%2C_Birr%2C_Offaly_1.jpg/220px-Great_Telescope%2C_Birr%2C_Offaly_1.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fe/Great_Telescope%2C_Birr%2C_Offaly_1.jpg/330px-Great_Telescope%2C_Birr%2C_Offaly_1.jpg 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fe/Great_Telescope%2C_Birr%2C_Offaly_1.jpg/440px-Great_Telescope%2C_Birr%2C_Offaly_1.jpg 2x" data-file-width="600" data-file-height="450" /></a><figcaption>The great telescope of <a href="/wiki/Birr_Castle" title="Birr Castle">Birr Castle</a>, the <a href="/wiki/Leviathan_of_Parsonstown" title="Leviathan of Parsonstown">Leviathan of Parsonstown</a>. Modern day remnants of the mirror and support structure.</figcaption></figure> <p>The idea that <a href="/wiki/Curved_mirrors" class="mw-redirect" title="Curved mirrors">curved mirrors</a> behave like lenses dates back at least to <a href="/wiki/Alhazen" class="mw-redirect" title="Alhazen">Alhazen</a>'s 11th century treatise on optics, works that had been widely disseminated in Latin translations in <a href="/wiki/Early_modern_Europe" title="Early modern Europe">early modern Europe</a>.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> Soon after the invention of the <a href="/wiki/Refracting_telescope" title="Refracting telescope">refracting telescope</a>, <a href="/wiki/Galileo" class="mw-redirect" title="Galileo">Galileo</a>, <a href="/wiki/Giovanni_Francesco_Sagredo" title="Giovanni Francesco Sagredo">Giovanni Francesco Sagredo</a>, 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.<sup id="cite_ref-Fred_Watson_2007_109_3-0" class="reference"><a href="#cite_note-Fred_Watson_2007_109-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> There were reports that the <a href="/wiki/Bologna" title="Bologna">Bolognese</a> Cesare Caravaggi had constructed one around 1626 and the Italian professor <a href="/wiki/Niccol%C3%B2_Zucchi" title="Niccolò Zucchi">Niccolò Zucchi</a>, 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.<sup id="cite_ref-Fred_Watson_2007_109_3-1" class="reference"><a href="#cite_note-Fred_Watson_2007_109-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The potential advantages of using <a href="/wiki/Parabolic_reflector" title="Parabolic reflector">parabolic mirrors</a>, primarily reduction of <a href="/wiki/Spherical_aberration" title="Spherical aberration">spherical aberration</a> with no <a href="/wiki/Chromatic_aberration" title="Chromatic aberration">chromatic aberration</a>, led to many proposed designs for reflecting telescopes.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> The most notable being <a href="/wiki/James_Gregory_(astronomer_and_mathematician)" class="mw-redirect" title="James Gregory (astronomer and mathematician)">James Gregory</a>, who published an innovative design for a ‘reflecting’ telescope in 1663. It would be ten years (1673), before the experimental scientist <a href="/wiki/Robert_Hooke" title="Robert Hooke">Robert Hooke</a> was able to build this type of telescope, which became known as the <a href="/wiki/Gregorian_telescope" title="Gregorian telescope">Gregorian telescope</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>Five years after Gregory designed his telescope and five years before Hooke built the first such Gregorian telescope, <a href="/wiki/Isaac_Newton" title="Isaac Newton">Isaac Newton</a> in 1668 built <a href="/wiki/Newton%27s_reflector" title="Newton's reflector">his own reflecting telescope</a>, which is generally acknowledged as the first reflecting telescope.<sup id="cite_ref-books.google.com_8-0" class="reference"><a href="#cite_note-books.google.com-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> It used a spherically ground metal <a href="/wiki/Primary_mirror" title="Primary mirror">primary mirror</a> and a small diagonal mirror in an optical configuration that has come to be known as the <a href="/wiki/Newtonian_telescope" title="Newtonian telescope">Newtonian telescope</a>. </p><p>Despite the theoretical advantages of the reflector design, the difficulty of construction and the poor performance of the <a href="/wiki/Speculum_metal" title="Speculum metal">speculum metal</a> 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 <a href="/wiki/Parabolic_reflector" title="Parabolic reflector">parabolic mirror</a> fabrication in the 18th century,<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> silver coated glass mirrors in the 19th century (built by <a href="/wiki/L%C3%A9on_Foucault" title="Léon Foucault">Léon Foucault</a> in 1858),<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> long-lasting aluminum coatings in the 20th century,<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Segmented_mirror" title="Segmented mirror">segmented mirrors</a> to allow larger diameters, and <a href="/wiki/Active_optics" title="Active optics">active optics</a> to compensate for gravitational deformation. A mid-20th century innovation was <a href="/wiki/Catadioptric_system" title="Catadioptric system">catadioptric</a> telescopes such as the <a href="/wiki/Schmidt_camera" title="Schmidt camera">Schmidt camera</a>, 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. </p><p>The late 20th century has seen the development of <a href="/wiki/Adaptive_optics" title="Adaptive optics">adaptive optics</a> and <a href="/wiki/Lucky_imaging" title="Lucky imaging">lucky imaging</a> to overcome the problems of <a href="/wiki/Astronomical_seeing" title="Astronomical seeing">seeing</a>, and reflecting telescopes are ubiquitous on <a href="/wiki/Space_telescope" title="Space telescope">space telescopes</a> and many types of <a href="/wiki/Spacecraft" title="Spacecraft">spacecraft</a> imaging devices. </p> <div class="mw-heading mw-heading2"><h2 id="Technical_considerations">Technical considerations</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=2" title="Edit section: Technical considerations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Gran_Telescopio_Canarias.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Gran_Telescopio_Canarias.jpg/200px-Gran_Telescopio_Canarias.jpg" decoding="async" width="200" height="217" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Gran_Telescopio_Canarias.jpg/300px-Gran_Telescopio_Canarias.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Gran_Telescopio_Canarias.jpg/400px-Gran_Telescopio_Canarias.jpg 2x" data-file-width="944" data-file-height="1024" /></a><figcaption><a href="/wiki/Gran_Telescopio_Canarias" title="Gran Telescopio Canarias">Gran Telescopio Canarias</a></figcaption></figure> <p>A curved <a href="/wiki/Primary_mirror" title="Primary mirror">primary mirror</a> is the reflector telescope's basic optical element that creates an image at the focal plane. The distance from the mirror to the focal plane is called the <a href="/wiki/Focal_length" title="Focal length">focal length</a>. Film or a digital sensor may be located here to record the image, or a <a href="/wiki/Secondary_mirror" title="Secondary mirror">secondary mirror</a> may be added to modify the optical characteristics and/or redirect the light to film, digital sensors, or an <a href="/wiki/Eyepiece" title="Eyepiece">eyepiece</a> for visual observation. </p><p>The primary mirror in most modern telescopes is composed of a solid glass <a href="/wiki/Cylinder_(geometry)" class="mw-redirect" title="Cylinder (geometry)">cylinder</a> whose front surface has been ground to a <a href="/wiki/Spherical_reflector" class="mw-redirect" title="Spherical reflector">spherical</a> or <a href="/wiki/Paraboloid_reflector" class="mw-redirect" title="Paraboloid reflector">parabolic</a> shape. A thin layer of <a href="/wiki/Aluminum" class="mw-redirect" title="Aluminum">aluminum</a> is <a href="/wiki/Vacuum_deposition" title="Vacuum deposition">vacuum deposited</a> onto the mirror, forming a highly reflective <a href="/wiki/First_surface_mirror" class="mw-redirect" title="First surface mirror">first surface mirror</a>. </p><p>Some telescopes use primary mirrors which are made differently. Molten glass is rotated to make its surface paraboloidal, and is kept rotating while it cools and solidifies. (See <a href="/wiki/Rotating_furnace" title="Rotating furnace">Rotating furnace</a>.) The resulting mirror shape approximates a desired paraboloid shape that requires minimal grinding and polishing to reach the exact figure needed.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Optical_errors">Optical errors</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=3" title="Edit section: Optical errors"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Reflecting telescopes, just like any other optical system, do not produce "perfect" images. The need to image objects at distances up to infinity, view them at different wavelengths of light, along with the requirement to have some way to view the image the primary mirror produces, means there is always some compromise in a reflecting telescope's optical design. </p> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Sirius_A_and_B_Hubble_photo.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Sirius_A_and_B_Hubble_photo.jpg/180px-Sirius_A_and_B_Hubble_photo.jpg" decoding="async" width="180" height="197" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Sirius_A_and_B_Hubble_photo.jpg/270px-Sirius_A_and_B_Hubble_photo.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Sirius_A_and_B_Hubble_photo.jpg/360px-Sirius_A_and_B_Hubble_photo.jpg 2x" data-file-width="369" data-file-height="403" /></a><figcaption>An image of <a href="/wiki/Sirius_A" class="mw-redirect" title="Sirius A">Sirius A</a> and <a href="/wiki/Sirius_B" class="mw-redirect" title="Sirius B">Sirius B</a> by the <a href="/wiki/Hubble_Space_Telescope" title="Hubble Space Telescope">Hubble Space Telescope</a>, showing <a href="/wiki/Diffraction_spike" title="Diffraction spike">diffraction spikes</a> and concentric <a href="/wiki/Airy_disk" title="Airy disk">diffraction rings</a>.</figcaption></figure> <p>Because the primary mirror focuses light to a common point in front of its own reflecting surface almost all reflecting telescope designs have a <a href="/wiki/Secondary_mirror" title="Secondary mirror">secondary mirror</a>, film holder, or detector near that focal point partially obstructing the light from reaching the primary mirror. Not only does this cause some reduction in the amount of light the system collects, it also causes a loss in contrast in the image due to <a href="/wiki/Diffraction" title="Diffraction">diffraction</a> effects of the obstruction as well as <a href="/wiki/Diffraction_spike" title="Diffraction spike">diffraction spikes</a> caused by most secondary support structures.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p><p>The use of mirrors avoids <a href="/wiki/Chromatic_aberration" title="Chromatic aberration">chromatic aberration</a> but they produce other types of <a href="/wiki/Aberration_in_optical_systems" class="mw-redirect" title="Aberration in optical systems">aberrations</a>. A simple <a href="/wiki/Spherical_mirror" class="mw-redirect" title="Spherical mirror">spherical mirror</a> cannot bring light from a distant object to a common focus since the reflection of light rays striking the mirror near its edge do not converge with those that reflect from nearer the center of the mirror, a defect called <a href="/wiki/Spherical_aberration" title="Spherical aberration">spherical aberration</a>. To avoid this problem most reflecting telescopes use <a href="/wiki/Parabolic_reflector" title="Parabolic reflector">parabolic shaped mirrors</a>, a shape that can focus all the light to a common focus. Parabolic mirrors work well with objects near the center of the image they produce, (light traveling parallel to the mirror's <a href="/wiki/Optical_axis" title="Optical axis">optical axis</a>), but towards the edge of that same field of view they suffer from off axis aberrations:<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <ul><li><a href="/wiki/Coma_(optics)" title="Coma (optics)">Coma</a> – an aberration where point sources (stars) at the center of the image are focused to a point but typically appears as "comet-like" radial smudges that get worse towards the edges of the image.</li> <li><a href="/wiki/Field_curvature" class="mw-redirect" title="Field curvature">Field curvature</a> – The best image plane is in general curved, which may not correspond to the detector's shape and leads to a focus error across the field. It is sometimes corrected by a field flattening lens.</li> <li><a href="/wiki/Astigmatism_(optical_systems)" title="Astigmatism (optical systems)">Astigmatism</a> – an <a href="/wiki/Azimuth" title="Azimuth">azimuthal</a> variation of focus around the aperture causing point source images off-axis to appear elliptical. Astigmatism is not usually a problem in a narrow <a href="/wiki/Field_of_view" title="Field of view">field of view</a>, but in a wide field image it gets rapidly worse and varies quadratically with field angle.</li> <li><a href="/wiki/Distortion_(optics)" title="Distortion (optics)">Distortion</a> – Distortion does not affect image quality (sharpness) but does affect object shapes. It is sometimes corrected by image processing.</li></ul> <p>There are reflecting telescope designs that use modified mirror surfaces (such as the <a href="/wiki/Ritchey%E2%80%93Chr%C3%A9tien_telescope" title="Ritchey–Chrétien telescope">Ritchey–Chrétien telescope</a>) or some form of correcting lens (such as <a href="/wiki/Catadioptric_system#Catadioptric_telescopes" title="Catadioptric system">catadioptric telescopes</a>) that correct some of these aberrations. </p> <div class="mw-heading mw-heading2"><h2 id="Use_in_astronomical_research">Use in astronomical research</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=4" title="Edit section: Use in astronomical research"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:James_Webb_Space_Telescope_Revealed_(26832090085).jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/James_Webb_Space_Telescope_Revealed_%2826832090085%29.jpg/220px-James_Webb_Space_Telescope_Revealed_%2826832090085%29.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/James_Webb_Space_Telescope_Revealed_%2826832090085%29.jpg/330px-James_Webb_Space_Telescope_Revealed_%2826832090085%29.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a2/James_Webb_Space_Telescope_Revealed_%2826832090085%29.jpg/440px-James_Webb_Space_Telescope_Revealed_%2826832090085%29.jpg 2x" data-file-width="4032" data-file-height="3024" /></a><figcaption>Main mirror of <a href="/wiki/James_Webb_Space_Telescope" title="James Webb Space Telescope">James Webb Space Telescope</a> assembled at <a href="/wiki/Goddard_Spaceflight_Center" class="mw-redirect" title="Goddard Spaceflight Center">Goddard Space Flight Center</a>, May 2016.</figcaption></figure> <p>Nearly all large research-grade astronomical telescopes are reflectors. There are several reasons for this: </p> <ul><li>Reflectors work in a wider <a href="/wiki/Spectrum_of_light" class="mw-redirect" title="Spectrum of light">spectrum of light</a> since certain wavelengths are absorbed when passing through glass elements like those found in a <a href="/wiki/Refractor" class="mw-redirect" title="Refractor">refractor</a> or in a <a href="/wiki/Catadioptric_telescope" class="mw-redirect" title="Catadioptric telescope">catadioptric telescope</a>.</li> <li>In a <a href="/wiki/Lens_(optics)" class="mw-redirect" title="Lens (optics)">lens</a> the entire volume of material has to be free of imperfection and inhomogeneities, whereas in a mirror, only one surface has to be perfectly polished.</li> <li>Light of different <a href="/wiki/Wavelength" title="Wavelength">wavelengths</a> travels through a medium other than <a href="/wiki/Vacuum" title="Vacuum">vacuum</a> at different speeds. This causes <a href="/wiki/Chromatic_aberration" title="Chromatic aberration">chromatic aberration</a>. Reducing this to acceptable levels usually involves a combination of two or three aperture sized lenses (see <a href="/wiki/Achromat" class="mw-redirect" title="Achromat">achromat</a> and <a href="/wiki/Apochromat" title="Apochromat">apochromat</a> for more details). The cost of such systems therefore scales significantly with aperture size. An image obtained from a mirror does not suffer from chromatic aberration to begin with, and the cost of the mirror scales much more modestly with its size.</li> <li>There are structural problems involved in manufacturing and manipulating large-aperture lenses. Since a lens can only be held in place by its edge, the center of a large lens will sag due to <a href="/wiki/Gravity" title="Gravity">gravity</a>, distorting the image it produces. The largest practical lens size in a refracting telescope is around 1 meter.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> In contrast, a mirror can be supported by the whole side opposite its reflecting face, allowing for reflecting telescope designs that can overcome gravitational sag. The largest reflector designs currently exceed 10 meters in diameter.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Reflecting_telescope_designs">Reflecting telescope designs</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=5" title="Edit section: Reflecting telescope designs"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Gregorian">Gregorian</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=6" title="Edit section: Gregorian"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Gregorian_telescope" title="Gregorian telescope">Gregorian telescope</a></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Gregorian_telescope.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/23/Gregorian_telescope.svg/500px-Gregorian_telescope.svg.png" decoding="async" width="500" height="154" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/23/Gregorian_telescope.svg/750px-Gregorian_telescope.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/23/Gregorian_telescope.svg/1000px-Gregorian_telescope.svg.png 2x" data-file-width="996" data-file-height="306" /></a><figcaption>Light path in a Gregorian telescope.</figcaption></figure> <p>The <b><a href="/wiki/Gregorian_telescope" title="Gregorian telescope">Gregorian telescope</a></b>, described by <a href="/wiki/Scotland" title="Scotland">Scottish</a> astronomer and mathematician <a href="/wiki/James_Gregory_(mathematician)" title="James Gregory (mathematician)">James Gregory</a> in his 1663 book <i>Optica Promota</i>, employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image, useful for terrestrial observations. Some small <a href="/wiki/Spotting_scope" title="Spotting scope">spotting scopes</a> are still built this way. There are several large modern telescopes that use a Gregorian configuration such as the <a href="/wiki/Vatican_Advanced_Technology_Telescope" title="Vatican Advanced Technology Telescope">Vatican Advanced Technology Telescope</a>, the <a href="/wiki/Magellan_telescopes" class="mw-redirect" title="Magellan telescopes">Magellan telescopes</a>, the <a href="/wiki/Large_Binocular_Telescope" title="Large Binocular Telescope">Large Binocular Telescope</a>, and the <a href="/wiki/Giant_Magellan_Telescope" title="Giant Magellan Telescope">Giant Magellan Telescope</a>. </p> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading3"><h3 id="Newtonian">Newtonian</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=7" title="Edit section: Newtonian"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Newtonian_telescope2.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/86/Newtonian_telescope2.svg/500px-Newtonian_telescope2.svg.png" decoding="async" width="500" height="226" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/86/Newtonian_telescope2.svg/750px-Newtonian_telescope2.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/86/Newtonian_telescope2.svg/1000px-Newtonian_telescope2.svg.png 2x" data-file-width="876" data-file-height="396" /></a><figcaption>Light path in a Newtonian telescope.</figcaption></figure> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Newtonian_telescope" title="Newtonian telescope">Newtonian telescope</a></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Schmidt%E2%80%93Newton_telescope" class="mw-redirect" title="Schmidt–Newton telescope">Schmidt–Newton telescope</a></div> <p>The <b><a href="/wiki/Newtonian_telescope" title="Newtonian telescope">Newtonian telescope</a></b> was the first successful reflecting telescope, completed by <a href="/wiki/Isaac_Newton" title="Isaac Newton">Isaac Newton</a> in 1668. It usually has a paraboloid primary mirror but at <a href="/wiki/F-number" title="F-number">focal ratios</a> of about f/10 or longer a spherical primary mirror can be sufficient for high visual resolution. A flat secondary mirror reflects the light to a focal plane at the side of the top of the telescope tube. It is one of the simplest and least expensive designs for a given size of primary, and is popular with <a href="/wiki/Amateur_telescope_making" title="Amateur telescope making">amateur telescope makers</a> as a home-build project. </p> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading3"><h3 id="The_Cassegrain_design_and_its_variations">The Cassegrain design and its variations</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=8" title="Edit section: The Cassegrain design and its variations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Cassegrain_Telescope.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Cassegrain_Telescope.svg/500px-Cassegrain_Telescope.svg.png" decoding="async" width="500" height="154" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Cassegrain_Telescope.svg/750px-Cassegrain_Telescope.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Cassegrain_Telescope.svg/1000px-Cassegrain_Telescope.svg.png 2x" data-file-width="1328" data-file-height="408" /></a><figcaption>Light path in a Cassegrain telescope.</figcaption></figure> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Cassegrain_reflector" title="Cassegrain reflector">Cassegrain reflector</a></div> <p>The <b>Cassegrain telescope</b> (sometimes called the "Classic Cassegrain") was first published in a 1672 design attributed to <a href="/wiki/Laurent_Cassegrain" title="Laurent Cassegrain">Laurent Cassegrain</a>. It has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. The folding and diverging effect of the secondary mirror creates a telescope with a long focal length while having a short tube length. </p> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading4"><h4 id="Ritchey–Chrétien"><span id="Ritchey.E2.80.93Chr.C3.A9tien"></span>Ritchey–Chrétien</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=9" title="Edit section: Ritchey–Chrétien"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Ritchey%E2%80%93Chr%C3%A9tien_telescope" title="Ritchey–Chrétien telescope">Ritchey–Chrétien telescope</a></div> <p>The <b>Ritchey–Chrétien</b> telescope, invented by <a href="/wiki/George_Willis_Ritchey" title="George Willis Ritchey">George Willis Ritchey</a> and <a href="/wiki/Henri_Chr%C3%A9tien" title="Henri Chrétien">Henri Chrétien</a> in the early 1910s, is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary). It is free of <a href="/wiki/Coma_(optics)" title="Coma (optics)">coma</a> and spherical aberration at a nearly flat focal plane if the primary and secondary curvature are properly <a href="/wiki/Figuring" title="Figuring">figured</a>, making it well suited for wide field and photographic observations.<sup id="cite_ref-Sacek1_18-0" class="reference"><a href="#cite_note-Sacek1-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> Almost every professional reflector telescope in the world is of the Ritchey–Chrétien design. </p> <div class="mw-heading mw-heading4"><h4 id="Three-mirror_anastigmat">Three-mirror anastigmat</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=10" title="Edit section: Three-mirror anastigmat"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Three-mirror_anastigmat" title="Three-mirror anastigmat">Three-mirror anastigmat</a></div> <p>Including a third curved mirror allows correction of the remaining distortion, astigmatism, from the Ritchey–Chrétien design. This allows much larger fields of view. </p> <div class="mw-heading mw-heading4"><h4 id="Dall–Kirkham"><span id="Dall.E2.80.93Kirkham"></span>Dall–Kirkham</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=11" title="Edit section: Dall–Kirkham"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Modified_Dall%E2%80%93Kirkham_telescope" title="Modified Dall–Kirkham telescope">Modified Dall–Kirkham telescope</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Large_1987_0528_0001_.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Large_1987_0528_0001_.jpg/220px-Large_1987_0528_0001_.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Large_1987_0528_0001_.jpg/330px-Large_1987_0528_0001_.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Large_1987_0528_0001_.jpg/440px-Large_1987_0528_0001_.jpg 2x" data-file-width="1536" data-file-height="1151" /></a><figcaption>Dall-Kirkham reflecting telescope, built by Horace Edward Dall</figcaption></figure> <p>The <b>Dall–Kirkham</b> Cassegrain telescope's design was created by Horace Dall in 1928 and took on the name in an article published in <i><a href="/wiki/Scientific_American" title="Scientific American">Scientific American</a></i> in 1930 following discussion between amateur astronomer Allan Kirkham and Albert G. Ingalls, the magazine editor at the time. It uses a concave <a href="/wiki/Ellipse" title="Ellipse">elliptical</a> primary mirror and a convex <a href="/wiki/Spherical" class="mw-redirect" title="Spherical">spherical</a> secondary. While this system is easier to grind than a classic Cassegrain or Ritchey–Chrétien system, it does not correct for off-axis coma. Field curvature is actually less than a classical Cassegrain. Because this is less noticeable at longer <a href="/wiki/Focal_ratio" class="mw-redirect" title="Focal ratio">focal ratios</a>, Dall–Kirkhams are seldom faster than f/15. </p> <div class="mw-heading mw-heading3"><h3 id="Off-axis_designs">Off-axis designs</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=12" title="Edit section: Off-axis designs"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are several designs that try to avoid obstructing the incoming light by eliminating the secondary or moving any secondary element off the primary mirror's <a href="/wiki/Optical_axis" title="Optical axis">optical axis</a>, commonly called <a href="/wiki/Off-axis_optical_system" title="Off-axis optical system">off-axis optical systems</a>. </p> <div class="mw-heading mw-heading4"><h4 id="Herschelian"><span class="anchor" id="Herschelian_telescope"></span>Herschelian</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=13" title="Edit section: Herschelian"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1237032888/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner img{background-color:white}}</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:254px;max-width:254px"><div class="trow"><div class="theader">Light paths</div></div><div class="trow"><div class="tsingle" style="width:252px;max-width:252px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Herschel-Lomonosov_reflecting_telescope.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Herschel-Lomonosov_reflecting_telescope.svg/250px-Herschel-Lomonosov_reflecting_telescope.svg.png" decoding="async" width="250" height="129" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Herschel-Lomonosov_reflecting_telescope.svg/375px-Herschel-Lomonosov_reflecting_telescope.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Herschel-Lomonosov_reflecting_telescope.svg/500px-Herschel-Lomonosov_reflecting_telescope.svg.png 2x" data-file-width="175" data-file-height="90" /></a></span></div><div class="thumbcaption">Herschelian telescope</div></div></div><div class="trow"><div class="tsingle" style="width:252px;max-width:252px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Off-axis_optical_telescope_diagram.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Off-axis_optical_telescope_diagram.svg/250px-Off-axis_optical_telescope_diagram.svg.png" decoding="async" width="250" height="112" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Off-axis_optical_telescope_diagram.svg/375px-Off-axis_optical_telescope_diagram.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Off-axis_optical_telescope_diagram.svg/500px-Off-axis_optical_telescope_diagram.svg.png 2x" data-file-width="226" data-file-height="101" /></a></span></div><div class="thumbcaption">Schiefspiegler telescope</div></div></div></div></div> <p>The <b>Herschelian</b> reflector is named after <a href="/wiki/William_Herschel" title="William Herschel">William Herschel</a>, who used this design to build very large telescopes including the <a href="/wiki/40-foot_telescope" title="40-foot telescope">40-foot telescope</a> in 1789. In the Herschelian reflector the primary mirror is tilted so the observer's head does not block the incoming light. Although this introduces geometrical aberrations, Herschel employed this design to avoid the use of a Newtonian secondary mirror since the <a href="/wiki/Speculum_metal" title="Speculum metal">speculum metal</a> mirrors of that time <a href="/wiki/Tarnish" title="Tarnish">tarnished</a> quickly and could only achieve 60% reflectivity.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Schiefspiegler">Schiefspiegler</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=14" title="Edit section: Schiefspiegler"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Schiefspiegler" title="Schiefspiegler">Schiefspiegler</a></div> <p>A variant of the Cassegrain, the Schiefspiegler telescope ("skewed" or "oblique reflector") uses tilted mirrors to avoid the secondary mirror casting a shadow on the primary. However, while eliminating diffraction patterns this leads to an increase in coma and astigmatism. These defects become manageable at large focal ratios — most Schiefspieglers use f/15 or longer, which tends to restrict useful observations to objects which fit in a moderate field of view. A 6" (150mm) f/15 telescope offers a maximum 0.75 degree field of view using 1.25" eyepieces. A number of variations are common, with varying numbers of mirrors of different types. The Kutter (named after its inventor <a href="/wiki/Anton_Kutter" title="Anton Kutter">Anton Kutter</a>) style uses a single concave primary, a convex secondary and a plano-convex lens between the secondary mirror and the focal plane, when needed (this is the case of the <i>catadioptric Schiefspiegler</i>). One variation of a multi-schiefspiegler uses a concave primary, convex secondary and a parabolic tertiary. One of the interesting aspects of some Schiefspieglers is that one of the mirrors can be involved in the light path twice — each light path reflects along a different meridional path. </p> <div class="mw-heading mw-heading4"><h4 id="Stevick-Paul">Stevick-Paul</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=15" title="Edit section: Stevick-Paul"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Stevick-Paul telescopes<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> are off-axis versions of Paul 3-mirror systems<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> with an added flat diagonal mirror. A convex secondary mirror is placed just to the side of the light entering the telescope, and positioned afocally so as to send parallel light on to the tertiary. The concave tertiary mirror is positioned exactly twice as far to the side of the entering beam as was the convex secondary, and its own radius of curvature distant from the secondary. Because the tertiary mirror receives parallel light from the secondary, it forms an image at its focus. The focal plane lies within the system of mirrors, but is accessible to the eye with the inclusion of a flat diagonal. The Stevick-Paul configuration results in all optical aberrations totaling zero to the third-order, except for the Petzval surface which is gently curved. </p> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading4"><h4 id="Yolo">Yolo</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=16" title="Edit section: Yolo"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The Yolo was developed by Arthur S. Leonard in the mid-1960s.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> Like the Schiefspiegler, it is an unobstructed, tilted reflector telescope. The original Yolo consists of a primary and secondary concave mirror, with the same curvature, and the same tilt to the main axis. Most Yolos use <a href="/wiki/Toroidal_reflector" title="Toroidal reflector">toroidal reflectors</a>. The Yolo design eliminates coma, but leaves significant astigmatism, which is reduced by deformation of the secondary mirror by some form of warping harness, or alternatively, polishing a toroidal figure into the secondary. Like Schiefspieglers, many Yolo variations have been pursued. The needed amount of toroidal shape can be transferred entirely or partially to the primary mirror. In large focal ratios optical assemblies, both primary and secondary mirror can be left spherical and a spectacle correcting lens is added between the secondary mirror and the focal plane (<i>catadioptric Yolo</i>). The addition of a convex, long focus tertiary mirror leads to Leonard's <i>Solano</i> configuration. The Solano telescope doesn't contain any toric surfaces. </p> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading3"><h3 id="Liquid-mirror_telescopes">Liquid-mirror telescopes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=17" title="Edit section: Liquid-mirror telescopes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Liquid-mirror_telescope" title="Liquid-mirror telescope">Liquid-mirror telescope</a></div> <p>One design of telescope uses a rotating mirror consisting of a liquid metal in a tray that is spun at constant speed. As the tray spins, the liquid forms a paraboloidal surface of essentially unlimited size. This allows making very big telescope mirrors (over 6 metres), but they are limited to use by <a href="/wiki/Zenith_telescope" title="Zenith telescope">zenith telescopes</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Focal_planes">Focal planes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=18" title="Edit section: Focal planes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Prime_focus">Prime focus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=19" title="Edit section: Prime focus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Prime_focus_telescope.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Prime_focus_telescope.svg/250px-Prime_focus_telescope.svg.png" decoding="async" width="250" height="86" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Prime_focus_telescope.svg/375px-Prime_focus_telescope.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Prime_focus_telescope.svg/500px-Prime_focus_telescope.svg.png 2x" data-file-width="1555" data-file-height="537" /></a><figcaption>A prime focus telescope design. The observer/camera is at the focal point (shown as a red X).</figcaption></figure> <p>In a <i>prime focus</i> design no secondary optics are used, the image is accessed at the <a href="/wiki/Focus_(optics)" title="Focus (optics)">focal point</a> of the <a href="/wiki/Primary_mirror" title="Primary mirror">primary mirror</a>. At the focal point is some type of structure for holding a film plate or electronic detector. In the past, in very large telescopes, an observer would sit inside the telescope in an "observing cage" to directly view the image or operate a camera.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> Nowadays <a href="/wiki/Charge-coupled_device" title="Charge-coupled device">CCD</a> cameras allow for remote operation of the telescope from almost anywhere in the world. The space available at prime focus is severely limited by the need to avoid obstructing the incoming light.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Radio_telescope" title="Radio telescope">Radio telescopes</a> often have a prime focus design. The mirror is replaced by a metal surface for reflecting <a href="/wiki/Radio_wave" title="Radio wave">radio waves</a>, and the observer is an <a href="/wiki/Antenna_(electronics)" class="mw-redirect" title="Antenna (electronics)">antenna</a>. </p> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Schmidt_camera" title="Schmidt camera">Schmidt camera</a></div> <div class="mw-heading mw-heading3"><h3 id="Cassegrain_focus">Cassegrain focus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=20" title="Edit section: Cassegrain focus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Cassegrain-Teleskop.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Cassegrain-Teleskop.svg/250px-Cassegrain-Teleskop.svg.png" decoding="async" width="250" height="97" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Cassegrain-Teleskop.svg/375px-Cassegrain-Teleskop.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Cassegrain-Teleskop.svg/500px-Cassegrain-Teleskop.svg.png 2x" data-file-width="267" data-file-height="104" /></a><figcaption>Cassegrain design</figcaption></figure> <p>For telescopes built to the Cassegrain design or other related designs, the image is formed behind the primary mirror, at the focal point of the <a href="/wiki/Secondary_mirror" title="Secondary mirror">secondary mirror</a>. An observer views through the rear of the telescope, or a camera or other instrument is mounted on the rear. Cassegrain focus is commonly used for amateur telescopes or smaller research telescopes. However, for large telescopes with correspondingly large instruments, an instrument at Cassegrain focus must move with the telescope as it slews; this places additional requirements on the strength of the instrument support structure, and potentially limits the movement of the telescope in order to avoid collision with obstacles such as walls or equipment inside the observatory. </p> <div class="mw-heading mw-heading3"><h3 id="Nasmyth_and_coudé_focus"><span id="Nasmyth_and_coud.C3.A9_focus"></span>Nasmyth and coudé focus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=21" title="Edit section: Nasmyth and coudé focus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Nasmyth-Telescope.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Nasmyth-Telescope.svg/250px-Nasmyth-Telescope.svg.png" decoding="async" width="250" height="119" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Nasmyth-Telescope.svg/375px-Nasmyth-Telescope.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Nasmyth-Telescope.svg/500px-Nasmyth-Telescope.svg.png 2x" data-file-width="231" data-file-height="110" /></a><figcaption>Nasmyth/coudé light path.</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Nasmyth">Nasmyth</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=22" title="Edit section: Nasmyth"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Nasmyth_telescope" title="Nasmyth telescope">Nasmyth telescope</a></div> <p>The <b>Nasmyth</b> design is similar to the Cassegrain except the light is not directed through a hole in the primary mirror; instead, a third mirror reflects the light to the side of the telescope to allow for the mounting of heavy instruments. This is a very common design in large research telescopes.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Coudé"><span id="Coud.C3.A9"></span>Coudé</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=23" title="Edit section: Coudé"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Adding further optics to a Nasmyth-style telescope to deliver the light (usually through the <a href="/wiki/Declination" title="Declination">declination</a> axis) to a fixed focus point that does not move as the telescope is reoriented gives a <b>coudé</b> focus (from the French word for elbow).<sup id="cite_ref-The_Coude_Focus_26-0" class="reference"><a href="#cite_note-The_Coude_Focus-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> The coudé focus gives a narrower field of view than a Nasmyth focus<sup id="cite_ref-The_Coude_Focus_26-1" class="reference"><a href="#cite_note-The_Coude_Focus-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> and is used with very heavy instruments that do not need a wide field of view. One such application is high-resolution <a href="/wiki/Spectrograph" class="mw-redirect" title="Spectrograph">spectrographs</a> that have large collimating mirrors (ideally with the same diameter as the telescope's primary mirror) and very long focal lengths. Such instruments could not withstand being moved, and adding mirrors to the light path to form a <i>coudé train</i>, diverting the light to a fixed position to such an instrument housed on or below the observing floor (and usually built as an unmoving integral part of the observatory building) was the only option. The <a href="/wiki/60-inch_Hale_telescope" class="mw-redirect" title="60-inch Hale telescope">60-inch Hale telescope</a> (1.5 m), <a href="/wiki/Hooker_Telescope" class="mw-redirect" title="Hooker Telescope">Hooker Telescope</a>, <a href="/wiki/200-inch_Hale_Telescope" class="mw-redirect" title="200-inch Hale Telescope">200-inch Hale Telescope</a>, <a href="/wiki/Shane_Telescope" class="mw-redirect" title="Shane Telescope">Shane Telescope</a>, and <a href="/wiki/Harlan_J._Smith_Telescope" title="Harlan J. Smith Telescope">Harlan J. Smith Telescope</a> all were built with coudé foci instrumentation. The development of <a href="/wiki/Echelle_grating" title="Echelle grating">echelle</a> spectrometers allowed high-resolution spectroscopy with a much more compact instrument, one which can sometimes be successfully mounted on the Cassegrain focus. Since inexpensive and adequately stable computer-controlled alt-az telescope mounts were developed in the 1980s, the Nasmyth design has generally supplanted the coudé focus for large telescopes. </p> <div class="mw-heading mw-heading3"><h3 id="Fibre-fed_spectrographs">Fibre-fed spectrographs</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=24" title="Edit section: Fibre-fed spectrographs"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>For instruments requiring very high stability, or that are very large and cumbersome, it is desirable to mount the instrument on a rigid structure, rather than moving it with the telescope. Whilst transmission of the full field of view would require a standard coudé focus, spectroscopy typically involves the measurement of only a few discrete objects, such as stars or galaxies. It is therefore feasible to collect light from these objects with <a href="/wiki/Optical_fiber" title="Optical fiber">optical fibers</a> at the telescope, placing the instrument at an arbitrary distance from the telescope. Examples of fiber-fed spectrographs include the planet-hunting spectrographs <a href="/wiki/High_Accuracy_Radial_Velocity_Planet_Searcher" title="High Accuracy Radial Velocity Planet Searcher">HARPS</a><sup id="cite_ref-HARPS_description_27-0" class="reference"><a href="#cite_note-HARPS_description-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> or <a href="/wiki/ESPRESSO" title="ESPRESSO">ESPRESSO</a>.<sup id="cite_ref-ESPRESSO_description_28-0" class="reference"><a href="#cite_note-ESPRESSO_description-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> </p><p>Additionally, the flexibility of optical fibers allow light to be collected from any focal plane; for example, the HARPS spectrograph utilises the Cassegrain focus of the <a href="/wiki/ESO_3.6_m_Telescope" title="ESO 3.6 m Telescope">ESO 3.6 m Telescope</a>,<sup id="cite_ref-HARPS_description_27-1" class="reference"><a href="#cite_note-HARPS_description-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> whilst the Prime Focus Spectrograph is connected to the prime focus of the <a href="/wiki/Subaru_Telescope" title="Subaru Telescope">Subaru telescope</a>.<sup id="cite_ref-PFS_Instrumentation_29-0" class="reference"><a href="#cite_note-PFS_Instrumentation-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=25" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Catadioptric_system#Catadioptric_telescopes" title="Catadioptric system">Catadioptric telescopes</a></li> <li><a href="/wiki/Honeycomb_mirror" title="Honeycomb mirror">Honeycomb mirror</a></li> <li><a href="/wiki/List_of_largest_optical_reflecting_telescopes" title="List of largest optical reflecting telescopes">List of largest optical reflecting telescopes</a></li> <li><a href="/wiki/List_of_largest_optical_telescopes_historically" title="List of largest optical telescopes historically">List of largest optical telescopes historically</a></li> <li><a href="/wiki/List_of_telescope_types" title="List of telescope types">List of telescope types</a></li> <li><a href="/wiki/Mirror_support_cell" title="Mirror support cell">Mirror support cell</a></li> <li><a href="/wiki/PLate_OPtimizer" title="PLate OPtimizer">PLate OPtimizer</a></li> <li><a href="/wiki/Refracting_telescope" title="Refracting telescope">Refracting telescope</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=26" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 25em;"> <ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFHenry_C._King1955" class="citation book cs1">Henry C. King (1955). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=KAWwzHlDVksC&q=history+of+the+telescope"><i>The History of the Telescope</i></a>. p. 74. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-486-43265-6" title="Special:BookSources/978-0-486-43265-6"><bdi>978-0-486-43265-6</bdi></a><span class="reference-accessdate">. Retrieved <span class="nowrap">2013-08-01</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+History+of+the+Telescope&rft.pages=74&rft.date=1955&rft.isbn=978-0-486-43265-6&rft.au=Henry+C.+King&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DKAWwzHlDVksC%26q%3Dhistory%2Bof%2Bthe%2Btelescope&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFred_Watson2007" class="citation book cs1">Fred Watson (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=2LZZginzib4C&pg=PA40"><i>Stargazer: The Life and Times of the Telescope</i></a>. Allen & Unwin. p. 108. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-74176-392-8" title="Special:BookSources/978-1-74176-392-8"><bdi>978-1-74176-392-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Stargazer%3A+The+Life+and+Times+of+the+Telescope&rft.pages=108&rft.pub=Allen+%26+Unwin&rft.date=2007&rft.isbn=978-1-74176-392-8&rft.au=Fred+Watson&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D2LZZginzib4C%26pg%3DPA40&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-Fred_Watson_2007_109-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-Fred_Watson_2007_109_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Fred_Watson_2007_109_3-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFred_Watson2007" class="citation book cs1">Fred Watson (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=2LZZginzib4C&pg=PA40"><i>Stargazer: The Life and Times of the Telescope</i></a>. Allen & Unwin. p. 109. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-74176-392-8" title="Special:BookSources/978-1-74176-392-8"><bdi>978-1-74176-392-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Stargazer%3A+The+Life+and+Times+of+the+Telescope&rft.pages=109&rft.pub=Allen+%26+Unwin&rft.date=2007&rft.isbn=978-1-74176-392-8&rft.au=Fred+Watson&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D2LZZginzib4C%26pg%3DPA40&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text">theoretical designs by <a href="/wiki/Bonaventura_Cavalieri" title="Bonaventura Cavalieri">Bonaventura Cavalieri</a>, <a href="/wiki/Marin_Mersenne" title="Marin Mersenne">Marin Mersenne</a>, and <a href="/wiki/James_Gregory_(astronomer_and_mathematician)" class="mw-redirect" title="James Gregory (astronomer and mathematician)">Gregory</a> among others</span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFred_Watson2007" class="citation book cs1">Fred Watson (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=2LZZginzib4C&pg=PA62"><i>Stargazer: The Life and Times of the Telescope</i></a>. Allen & Unwin. p. 117. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-74176-392-8" title="Special:BookSources/978-1-74176-392-8"><bdi>978-1-74176-392-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Stargazer%3A+The+Life+and+Times+of+the+Telescope&rft.pages=117&rft.pub=Allen+%26+Unwin&rft.date=2007&rft.isbn=978-1-74176-392-8&rft.au=Fred+Watson&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D2LZZginzib4C%26pg%3DPA62&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFHenry_C._King2003" class="citation book cs1">Henry C. King (2003). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=KAWwzHlDVksC&pg=PR1"><i>The History of the Telescope</i></a>. Courier Corporation. p. 71. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-486-43265-6" title="Special:BookSources/978-0-486-43265-6"><bdi>978-0-486-43265-6</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+History+of+the+Telescope&rft.pages=71&rft.pub=Courier+Corporation&rft.date=2003&rft.isbn=978-0-486-43265-6&rft.au=Henry+C.+King&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DKAWwzHlDVksC%26pg%3DPR1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20170117064000/http://www.nms.ac.uk/explore/stories/science-and-technology/reflecting-telescope/telescopes/james-gregory/">"Explore, National Museums Scotland"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.nms.ac.uk/explore/stories/science-and-technology/reflecting-telescope/telescopes/james-gregory/">the original</a> on 2017-01-17<span class="reference-accessdate">. Retrieved <span class="nowrap">2016-11-15</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Explore%2C+National+Museums+Scotland&rft_id=http%3A%2F%2Fwww.nms.ac.uk%2Fexplore%2Fstories%2Fscience-and-technology%2Freflecting-telescope%2Ftelescopes%2Fjames-gregory%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-books.google.com-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-books.google.com_8-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFA._Rupert_Hall1996" class="citation book cs1">A. Rupert Hall (1996). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/isaacnewtonadven0000hall"><i>Isaac Newton: Adventurer in Thought</i></a></span>. Cambridge University Press. p. <a rel="nofollow" class="external text" href="https://archive.org/details/isaacnewtonadven0000hall/page/67">67</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-521-56669-8" title="Special:BookSources/978-0-521-56669-8"><bdi>978-0-521-56669-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Isaac+Newton%3A+Adventurer+in+Thought&rft.pages=67&rft.pub=Cambridge+University+Press&rft.date=1996&rft.isbn=978-0-521-56669-8&rft.au=A.+Rupert+Hall&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fisaacnewtonadven0000hall&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text">Parabolic mirrors were used much earlier, but <a href="/wiki/James_Short_(mathematician)" title="James Short (mathematician)">James Short</a> perfected their construction. See <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20090131173814/http://www.astro.lsa.umich.edu/undergrad/Labs/optics/Reflectors.html">"Reflecting Telescopes (Newtonian Type)"</a>. Astronomy Department, University of Michigan. Archived from <a rel="nofollow" class="external text" href="http://www.astro.lsa.umich.edu/undergrad/Labs/optics/Reflectors.html">the original</a> on 2009-01-31.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Reflecting+Telescopes+%28Newtonian+Type%29&rft.pub=Astronomy+Department%2C+University+of+Michigan&rft_id=http%3A%2F%2Fwww.astro.lsa.umich.edu%2Fundergrad%2FLabs%2Foptics%2FReflectors.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLequeux2017" class="citation journal cs1">Lequeux, James (2017-01-01). <a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2017LAstr.131a..28L">"The Paris Observatory has 350 years"</a>. <i>L'Astronomie</i>. <b>131</b>: 28–37. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2017LAstr.131a..28L">2017LAstr.131a..28L</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0004-6302">0004-6302</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=L%27Astronomie&rft.atitle=The+Paris+Observatory+has+350+years&rft.volume=131&rft.pages=28-37&rft.date=2017-01-01&rft.issn=0004-6302&rft_id=info%3Abibcode%2F2017LAstr.131a..28L&rft.aulast=Lequeux&rft.aufirst=James&rft_id=https%3A%2F%2Fui.adsabs.harvard.edu%2Fabs%2F2017LAstr.131a..28L&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text">Silvering on a reflecting telescope was introduced by <a href="/wiki/L%C3%A9on_Foucault" title="Léon Foucault">Léon Foucault</a> in 1857, see <a rel="nofollow" class="external text" href="http://www.madehow.com/inventorbios/39/Jean-Bernard-L-on-Foucault.html">madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819–1868)</a>, and the adoption of long lasting aluminized coatings on reflector mirrors in 1932. <a rel="nofollow" class="external text" href="http://www.cambridge.org/uk/astronomy/features/amateur/files/p28-4.pdf">Bakich sample pages Chapter 2, Page 3 <i>"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."</i></a></span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRay_VillardLeonello_CalvettiLorenzo_Cecchi2001" class="citation book cs1">Ray Villard; Leonello Calvetti; Lorenzo Cecchi (2001). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=BA4riazAF5sC&pg=PA21"><i>Large Telescopes: Inside and Out</i></a>. The Rosen Publishing Group, Inc. p. 21. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-8239-6110-8" title="Special:BookSources/978-0-8239-6110-8"><bdi>978-0-8239-6110-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Large+Telescopes%3A+Inside+and+Out&rft.pages=21&rft.pub=The+Rosen+Publishing+Group%2C+Inc&rft.date=2001&rft.isbn=978-0-8239-6110-8&rft.au=Ray+Villard&rft.au=Leonello+Calvetti&rft.au=Lorenzo+Cecchi&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DBA4riazAF5sC%26pg%3DPA21&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/c-o%27s.html">Rodger W. Gordon, "Central Obstructions and their effect on image contrast" brayebrookobservatory.org</a></span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://spider.seds.org/scopes/obstruct.html">"Obstruction" in optical instruments</a></span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://farside.ph.utexas.edu/teaching/316/lectures/node136.html">Richard Fitzpatrick, Spherical Mirrors, farside.ph.utexas.edu</a></span> </li> <li id="cite_note-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-16">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20100505062511/http://www.vikdhillon.staff.shef.ac.uk/teaching/phy105/telescopes/phy105_tel_reflectors.html">"Vik Dhillon, reflectors, vikdhillon.staff.shef.ac.uk"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.vikdhillon.staff.shef.ac.uk/teaching/phy105/telescopes/phy105_tel_reflectors.html">the original</a> on 2010-05-05<span class="reference-accessdate">. Retrieved <span class="nowrap">2010-04-06</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Vik+Dhillon%2C+reflectors%2C+vikdhillon.staff.shef.ac.uk&rft_id=http%3A%2F%2Fwww.vikdhillon.staff.shef.ac.uk%2Fteaching%2Fphy105%2Ftelescopes%2Fphy105_tel_reflectors.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFStan_Gibilisco2002" class="citation book cs1">Stan Gibilisco (2002). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/physicsdemystifi0000gibi"><i>Physics Demystified</i></a></span>. Mcgraw-hill. p. <a rel="nofollow" class="external text" href="https://archive.org/details/physicsdemystifi0000gibi/page/515">515</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-07-138201-4" title="Special:BookSources/978-0-07-138201-4"><bdi>978-0-07-138201-4</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Physics+Demystified&rft.pages=515&rft.pub=Mcgraw-hill&rft.date=2002&rft.isbn=978-0-07-138201-4&rft.au=Stan+Gibilisco&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fphysicsdemystifi0000gibi&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-Sacek1-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-Sacek1_18-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSacek2006" class="citation web cs1">Sacek, Vladimir (July 14, 2006). <a rel="nofollow" class="external text" href="http://www.telescope-optics.net/classical_and_aplanatic.htm">"8.2.2 Classical and aplanatic two-mirror systems"</a>. <i>Notes on AMATEUR TELESCOPE OPTICS</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2009-06-22</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Notes+on+AMATEUR+TELESCOPE+OPTICS&rft.atitle=8.2.2+Classical+and+aplanatic+two-mirror+systems&rft.date=2006-07-14&rft.aulast=Sacek&rft.aufirst=Vladimir&rft_id=http%3A%2F%2Fwww.telescope-optics.net%2Fclassical_and_aplanatic.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-19">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://catalogue.museogalileo.it/indepth/Telescope.html">catalogue.museogalileo.it - Institute and Museum of the History of Science - Florence, Italy, Telescope, glossary</a></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.amsky.com/atm/telescopes/spscopes/spt.html">Stevick-Paul Telescopes by Dave Stevick</a></span> </li> <li id="cite_note-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-21">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPaul1935" class="citation journal cs1">Paul, M. (1935). "Systèmes correcteurs pour réflecteurs astronomiques". <i><a href="/w/index.php?title=Revue_d%27Optique_Th%C3%A9orique_et_Instrumentale&action=edit&redlink=1" class="new" title="Revue d'Optique Théorique et Instrumentale (page does not exist)">Revue d'Optique Théorique et Instrumentale</a></i>. <b>14</b> (5): 169–202.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Revue+d%27Optique+Th%C3%A9orique+et+Instrumentale&rft.atitle=Syst%C3%A8mes+correcteurs+pour+r%C3%A9flecteurs+astronomiques&rft.volume=14&rft.issue=5&rft.pages=169-202&rft.date=1935&rft.aulast=Paul&rft.aufirst=M.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-22">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20030302111137/http://www.atmsite.org/contrib/Holm/yolo/index.html">Arthur S. Leonard THE YOLO REFLECTOR</a></span> </li> <li id="cite_note-23"><span class="mw-cite-backlink"><b><a href="#cite_ref-23">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFW._Patrick_McCray2004" class="citation book cs1">W. Patrick McCray (2004). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=9mUL9dGn9V4C&pg=PA27"><i>Giant Telescopes: Astronomical Ambition and the Promise of Technology</i></a>. Harvard University Press. p. 27. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-674-01147-2" title="Special:BookSources/978-0-674-01147-2"><bdi>978-0-674-01147-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Giant+Telescopes%3A+Astronomical+Ambition+and+the+Promise+of+Technology&rft.pages=27&rft.pub=Harvard+University+Press&rft.date=2004&rft.isbn=978-0-674-01147-2&rft.au=W.+Patrick+McCray&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D9mUL9dGn9V4C%26pg%3DPA27&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-24">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.ucolick.org/public/telescopes/shane.html#prime">"Prime Focus"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Prime+Focus&rft_id=http%3A%2F%2Fwww.ucolick.org%2Fpublic%2Ftelescopes%2Fshane.html%23prime&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-25"><span class="mw-cite-backlink"><b><a href="#cite_ref-25">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGeoff_Andersen2007" class="citation book cs1">Geoff Andersen (2007). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/telescopeitshist00ande"><i>The Telescope: Its History, Technology, and Future</i></a></span>. Princeton University Press. p. <a rel="nofollow" class="external text" href="https://archive.org/details/telescopeitshist00ande/page/103">103</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-691-12979-2" title="Special:BookSources/978-0-691-12979-2"><bdi>978-0-691-12979-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Telescope%3A+Its+History%2C+Technology%2C+and+Future&rft.pages=103&rft.pub=Princeton+University+Press&rft.date=2007&rft.isbn=978-0-691-12979-2&rft.au=Geoff+Andersen&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Ftelescopeitshist00ande&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-The_Coude_Focus-26"><span class="mw-cite-backlink">^ <a href="#cite_ref-The_Coude_Focus_26-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-The_Coude_Focus_26-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://mthamilton.ucolick.org/public/tele_inst/3m/coude.html">"The Coude Focus"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+Coude+Focus&rft_id=http%3A%2F%2Fmthamilton.ucolick.org%2Fpublic%2Ftele_inst%2F3m%2Fcoude.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-HARPS_description-27"><span class="mw-cite-backlink">^ <a href="#cite_ref-HARPS_description_27-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-HARPS_description_27-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.eso.org/sci/facilities/lasilla/instruments/harps/inst/description.html">"HARPS Instrument Description"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=HARPS+Instrument+Description&rft_id=https%3A%2F%2Fwww.eso.org%2Fsci%2Ffacilities%2Flasilla%2Finstruments%2Fharps%2Finst%2Fdescription.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-ESPRESSO_description-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-ESPRESSO_description_28-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.eso.org/sci/facilities/develop/instruments/espresso.html">"ESPRESSO Instrument Description"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=ESPRESSO+Instrument+Description&rft_id=https%3A%2F%2Fwww.eso.org%2Fsci%2Ffacilities%2Fdevelop%2Finstruments%2Fespresso.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> <li id="cite_note-PFS_Instrumentation-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-PFS_Instrumentation_29-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pfs.ipmu.jp/instrumentation.html">"Subaru PFS Instrumentation"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Subaru+PFS+Instrumentation&rft_id=http%3A%2F%2Fpfs.ipmu.jp%2Finstrumentation.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AReflecting+telescope" class="Z3988"></span></span> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Reflecting_telescope&action=edit&section=27" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output .side-box-abovebelow,.mw-parser-output .side-box-text{padding:0.25em 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src="//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/RocketSunIcon.svg/19px-RocketSunIcon.svg.png" decoding="async" width="19" height="19" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/RocketSunIcon.svg/29px-RocketSunIcon.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/d6/RocketSunIcon.svg/38px-RocketSunIcon.svg.png 2x" data-file-width="128" data-file-height="128" /></span></span> </span><a href="/wiki/Portal:Spaceflight" title="Portal:Spaceflight">Spaceflight</a></li><li class="portal-bar-item"><span class="nowrap"><span typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Earth-moon.jpg/21px-Earth-moon.jpg" decoding="async" width="21" height="17" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Earth-moon.jpg/32px-Earth-moon.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Earth-moon.jpg/42px-Earth-moon.jpg 2x" data-file-width="3000" 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