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Available in 51 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-51" 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">51 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Fokus" title="Fokus – Afrikaans" lang="af" hreflang="af" data-title="Fokus" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target"><span>Afrikaans</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%A8%D8%A4%D8%B1%D8%A9_%D8%A7%D9%84%D8%B9%D8%AF%D8%B3%D8%A9" title="بؤرة العدسة – Arabic" lang="ar" hreflang="ar" data-title="بؤرة العدسة" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%A4%D0%BE%D0%BA%D1%83%D1%81_(%D1%84%D1%96%D0%B7%D1%96%D0%BA%D0%B0)" title="Фокус (фізіка) – Belarusian" lang="be" hreflang="be" data-title="Фокус (фізіка)" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%A4%D0%BE%D0%BA%D1%83%D1%81_(%D0%BE%D0%BF%D1%82%D0%B8%D0%BA%D0%B0)" title="Фокус (оптика) – Bulgarian" lang="bg" hreflang="bg" data-title="Фокус (оптика)" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Fokus" title="Fokus – Bosnian" lang="bs" hreflang="bs" data-title="Fokus" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Focus_(%C3%B2ptica)" title="Focus (òptica) – Catalan" lang="ca" hreflang="ca" data-title="Focus (òptica)" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Fokus" title="Fokus – German" lang="de" hreflang="de" data-title="Fokus" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Fookus" title="Fookus – Estonian" lang="et" hreflang="et" data-title="Fookus" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Foco_(%C3%B3ptica)" title="Foco (óptica) – Spanish" lang="es" hreflang="es" data-title="Foco (óptica)" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Fokuso_(optiko)" title="Fokuso (optiko) – Esperanto" lang="eo" hreflang="eo" data-title="Fokuso (optiko)" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Foku_(optika)" title="Foku (optika) – Basque" lang="eu" hreflang="eu" data-title="Foku (optika)" 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/%DA%A9%D8%A7%D9%86%D9%88%D9%86_%D8%B9%D8%AF%D8%B3%DB%8C" title="کانون عدسی – Persian" lang="fa" hreflang="fa" data-title="کانون عدسی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Foyer_(optique)" title="Foyer (optique) – French" lang="fr" hreflang="fr" data-title="Foyer (optique)" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/F%C3%B3cas_(optaic)" title="Fócas (optaic) – Irish" lang="ga" hreflang="ga" data-title="Fócas (optaic)" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%B4%88%EC%A0%90_(%EA%B4%91%ED%95%99)" title="초점 (광학) – Korean" lang="ko" hreflang="ko" data-title="초점 (광학)" 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/%D4%BF%D5%AB%D5%A6%D5%A1%D5%AF%D5%A5%D5%BF" title="Կիզակետ – Armenian" lang="hy" hreflang="hy" data-title="Կիզակետ" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/%C5%BDari%C5%A1te" title="Žarište – Croatian" lang="hr" hreflang="hr" data-title="Žarište" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-io mw-list-item"><a href="https://io.wikipedia.org/wiki/Foko_(optiko)" title="Foko (optiko) – Ido" lang="io" hreflang="io" data-title="Foko (optiko)" data-language-autonym="Ido" data-language-local-name="Ido" class="interlanguage-link-target"><span>Ido</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Titik_api" title="Titik api – Indonesian" lang="id" hreflang="id" data-title="Titik api" 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/Fuoco_(ottica)" title="Fuoco (ottica) – Italian" lang="it" hreflang="it" data-title="Fuoco (ottica)" 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%9E%D7%95%D7%A7%D7%93_(%D7%90%D7%95%D7%A4%D7%98%D7%99%D7%A7%D7%94)" title="מוקד (אופטיקה) – Hebrew" lang="he" hreflang="he" data-title="מוקד (אופטיקה)" 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%A4%D0%BE%D0%BA%D1%83%D1%81_(%D1%84%D0%B8%D0%B7%D0%B8%D0%BA%D0%B0)" title="Фокус (физика) – Kazakh" lang="kk" hreflang="kk" data-title="Фокус (физика)" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Fokuss_(optika)" title="Fokuss (optika) – Latvian" lang="lv" hreflang="lv" data-title="Fokuss (optika)" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lb mw-list-item"><a href="https://lb.wikipedia.org/wiki/Fokus" title="Fokus – Luxembourgish" lang="lb" hreflang="lb" data-title="Fokus" data-language-autonym="Lëtzebuergesch" data-language-local-name="Luxembourgish" class="interlanguage-link-target"><span>Lëtzebuergesch</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%96%D0%B0%D1%80%D0%B8%D1%88%D1%82%D0%B5_(%D0%BE%D0%BF%D1%82%D0%B8%D0%BA%D0%B0)" title="Жариште (оптика) – Macedonian" lang="mk" hreflang="mk" data-title="Жариште (оптика)" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%AB%E0%B5%8B%E0%B4%95%E0%B5%8D%E0%B4%95%E0%B4%B8%E0%B5%8D_(%E0%B4%AA%E0%B5%8D%E0%B4%B0%E0%B4%95%E0%B4%BE%E0%B4%B6%E0%B4%B6%E0%B4%BE%E0%B4%B8%E0%B5%8D%E0%B4%A4%E0%B5%8D%E0%B4%B0%E0%B4%82)" title="ഫോക്കസ് (പ്രകാശശാസ്ത്രം) – Malayalam" lang="ml" hreflang="ml" data-title="ഫോക്കസ് (പ്രകാശശാസ്ത്രം)" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%A4%D0%BE%D0%BA%D1%83%D1%81_(%D0%BE%D0%BF%D1%82%D0%B8%D0%BA)" title="Фокус (оптик) – Mongolian" lang="mn" hreflang="mn" data-title="Фокус (оптик)" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Brandpunt_(optica)" title="Brandpunt (optica) – Dutch" lang="nl" hreflang="nl" data-title="Brandpunt (optica)" 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/%E7%84%A6%E7%82%B9_(%E5%85%89%E5%AD%A6)" title="焦点 (光学) – Japanese" lang="ja" hreflang="ja" data-title="焦点 (光学)" 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/Fokus_(optikk)" title="Fokus (optikk) – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Fokus (optikk)" 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/Fokus_i_fysikk" title="Fokus i fysikk – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Fokus i fysikk" 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-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/Fokus" title="Fokus – Uzbek" lang="uz" hreflang="uz" data-title="Fokus" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="Uzbek" class="interlanguage-link-target"><span>Oʻzbekcha / ўзбекча</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Ognisko_(optyka)" title="Ognisko (optyka) – Polish" lang="pl" hreflang="pl" data-title="Ognisko (optyka)" 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/Foco" title="Foco – Portuguese" lang="pt" hreflang="pt" data-title="Foco" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Focar_(optic%C4%83)" title="Focar (optică) – Romanian" lang="ro" hreflang="ro" data-title="Focar (optică)" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%A4%D0%BE%D0%BA%D1%83%D1%81_(%D1%84%D0%B8%D0%B7%D0%B8%D0%BA%D0%B0)" title="Фокус (физика) – Russian" lang="ru" hreflang="ru" data-title="Фокус (физика)" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Focus_(optics)" title="Focus (optics) – Simple English" lang="en-simple" hreflang="en-simple" data-title="Focus (optics)" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Ohnisko_(optika)" title="Ohnisko (optika) – Slovak" lang="sk" hreflang="sk" data-title="Ohnisko (optika)" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Gori%C5%A1%C4%8De_(optika)" title="Gorišče (optika) – Slovenian" lang="sl" hreflang="sl" data-title="Gorišče (optika)" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%A4%D0%BE%D0%BA%D1%83%D1%81_(%D0%BE%D0%BF%D1%82%D0%B8%D0%BA%D0%B0)" title="Фокус (оптика) – Serbian" lang="sr" hreflang="sr" data-title="Фокус (оптика)" 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-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Fokus" title="Fokus – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Fokus" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Polttopiste" title="Polttopiste – Finnish" lang="fi" hreflang="fi" data-title="Polttopiste" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Fokus_(optik)" title="Fokus (optik) – Swedish" lang="sv" hreflang="sv" data-title="Fokus (optik)" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%95%E0%AF%81%E0%AE%B5%E0%AE%BF%E0%AE%AF%E0%AE%AE%E0%AF%8D_(%E0%AE%92%E0%AE%B3%E0%AE%BF%E0%AE%AF%E0%AE%BF%E0%AE%AF%E0%AE%B2%E0%AF%8D)" title="குவியம் (ஒளியியல்) – Tamil" 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searchaux" style="display:none">Point in an optical system where light rays originating from a point on the object converge</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">For eye focus, see <a href="/wiki/Accommodation_(eye)" class="mw-redirect" title="Accommodation (eye)">Accommodation (eye)</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Focus_(optics)" title="Special:EditPage/Focus (optics)">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and removed.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22Focus%22+optics">"Focus" optics</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22Focus%22+optics+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22Focus%22+optics&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22Focus%22+optics+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22Focus%22+optics">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22Focus%22+optics&acc=on&wc=on">JSTOR</a></span></small></span> <span class="date-container"><i>(<span class="date">October 2015</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Focusing_on_retina.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Focusing_on_retina.svg/220px-Focusing_on_retina.svg.png" decoding="async" width="220" height="141" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Focusing_on_retina.svg/330px-Focusing_on_retina.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Focusing_on_retina.svg/440px-Focusing_on_retina.svg.png 2x" data-file-width="294" data-file-height="188" /></a><figcaption><a href="/wiki/Accommodation_(eye)" class="mw-redirect" title="Accommodation (eye)">Eye focusing</a> ideally collects all light rays from a point on an object into a corresponding point on the <a href="/wiki/Retina" title="Retina">retina</a>.</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:FocusDemonstration-BambooRooftop.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/FocusDemonstration-BambooRooftop.jpg/220px-FocusDemonstration-BambooRooftop.jpg" decoding="async" width="220" height="74" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/FocusDemonstration-BambooRooftop.jpg/330px-FocusDemonstration-BambooRooftop.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/22/FocusDemonstration-BambooRooftop.jpg/440px-FocusDemonstration-BambooRooftop.jpg 2x" data-file-width="7744" data-file-height="2592" /></a><figcaption>A demonstration of camera focus on different distances, showing a bamboo rooftop</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:DOF-ShallowDepthofField.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/38/DOF-ShallowDepthofField.jpg/220px-DOF-ShallowDepthofField.jpg" decoding="async" width="220" height="158" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/38/DOF-ShallowDepthofField.jpg/330px-DOF-ShallowDepthofField.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/38/DOF-ShallowDepthofField.jpg/440px-DOF-ShallowDepthofField.jpg 2x" data-file-width="997" data-file-height="717" /></a><figcaption>Text on a page that is partially in focus, but mostly not in varying degrees</figcaption></figure> <p>In <a href="/wiki/Geometrical_optics" title="Geometrical optics">geometrical optics</a>, a <b>focus</b>, also called an <b>image point</b>, is a point where <a href="/wiki/Ray_(optics)" title="Ray (optics)">light rays</a> originating from a point on the object <a href="/wiki/Vergence_(optics)" title="Vergence (optics)">converge</a>.<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> Although the focus is conceptually a point, physically the focus has a spatial extent, called the <a href="/wiki/Circle_of_confusion" title="Circle of confusion">blur circle</a>. This non-ideal focusing may be caused by <a href="/wiki/Optical_aberration" title="Optical aberration">aberrations</a> of the imaging optics. Even in the absence of aberrations, the smallest possible blur circle is the <a href="/wiki/Airy_disc" class="mw-redirect" title="Airy disc">Airy disc</a> caused by <a href="/wiki/Diffraction" title="Diffraction">diffraction</a> from the optical system's <a href="/wiki/Aperture" title="Aperture">aperture</a>; diffraction is the ultimate limit to the light focusing ability of any optical system. Aberrations tend to worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures. </p><p>An image, or image point or region, is <b>in focus</b> if light from object points is converged almost as much as possible in the image, and <a href="/wiki/Defocus_aberration" title="Defocus aberration">out of focus</a> if light is not well converged. The border between these is sometimes defined using a "<a href="/wiki/Circle_of_confusion" title="Circle of confusion">circle of confusion</a>" criterion. </p><p>A <b>principal focus</b> or <b>focal point</b> is a special focus: </p> <ul><li>For a <a href="/wiki/Lens_(optics)" class="mw-redirect" title="Lens (optics)">lens</a>, or a <a href="/wiki/Curved_mirror" title="Curved mirror">spherical or parabolic mirror</a>, it is a point onto which <a href="/wiki/Collimated_light" class="mw-redirect" title="Collimated light">collimated light</a> parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal points – one on each side. The distance in air from the lens or mirror's <a href="/wiki/Principal_plane" class="mw-redirect" title="Principal plane">principal plane</a> to the focus is called the <i><a href="/wiki/Focal_length" title="Focal length">focal length</a></i>.</li> <li><a href="/wiki/Ellipse" title="Ellipse">Elliptical</a> mirrors have two focal points: light that passes through one of these before striking the mirror is reflected such that it passes through the other.</li> <li>The focus of a <a href="/wiki/Hyperbola" title="Hyperbola">hyperbolic</a> <a href="/wiki/Mirror" title="Mirror">mirror</a> is either of two points which have the property that light from one is reflected as if it came from the other.</li></ul> <p><a href="/wiki/Vergence_(optics)" title="Vergence (optics)">Diverging</a> (negative) lenses and <a href="/wiki/Convex_mirrors" class="mw-redirect" title="Convex mirrors">convex mirrors</a> do not focus a collimated beam to a point. Instead, the focus is the point from which the light appears to be emanating, after it travels through the lens or reflects from the mirror. A convex parabolic mirror will reflect a beam of collimated light to make it appear as if it were radiating from the focal point, or conversely, reflect rays directed toward the <a href="/wiki/Focus_(geometry)" title="Focus (geometry)">focus</a> as a collimated beam. A convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex <a href="/wiki/Hyperbola" title="Hyperbola">hyperbolic</a> <a href="/wiki/Mirror" title="Mirror">mirror</a> will reflect rays emanating from the <a href="/wiki/Focus_(geometry)" title="Focus (geometry)">focal point</a> in front of the mirror as if they were emanating from the focal point behind the mirror. Conversely, it can focus rays directed at the focal point that is behind the mirror towards the focal point that is in front of the mirror as in a <a href="/wiki/Cassegrain_reflector" title="Cassegrain reflector">Cassegrain telescope</a>. </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=Focus_(optics)&action=edit&section=1" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Autofocus" title="Autofocus">Autofocus</a></li> <li><a href="/wiki/Cardinal_point_(optics)" title="Cardinal point (optics)">Cardinal point (optics)</a></li> <li><a href="/wiki/Defocus_aberration" title="Defocus aberration">Defocus aberration</a></li> <li><a href="/wiki/Depth_of_field" title="Depth of field">Depth of field</a></li> <li><a href="/wiki/Depth_of_focus" title="Depth of focus">Depth of focus</a></li> <li><a href="/wiki/Far_point" title="Far point">Far point</a></li> <li><a href="/wiki/Focus_(geometry)" title="Focus (geometry)">Focus (geometry)</a></li> <li><a href="/wiki/Fixed_focus" class="mw-redirect" title="Fixed focus">Fixed focus</a></li> <li><a href="/wiki/Bokeh" title="Bokeh">Bokeh</a></li> <li><a href="/wiki/Focus_stacking" title="Focus stacking">Focus stacking</a></li> <li><a href="/wiki/Focal_plane" class="mw-redirect" title="Focal plane">Focal plane</a></li> <li><a href="/wiki/Manual_focus" title="Manual focus">Manual focus</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=Focus_(optics)&action=edit&section=2" 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"> <div class="mw-references-wrap"><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 class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20080302163401/http://www.charfac.umn.edu/glossary/f.html">"Standard Microscopy Terminology"</a>. <i>University of Minnesota Characterization Facility website</i>. Archived from <a rel="nofollow" class="external text" href="http://www.charfac.umn.edu/glossary/f.html">the original</a> on 2008-03-02<span class="reference-accessdate">. Retrieved <span class="nowrap">2006-04-21</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=University+of+Minnesota+Characterization+Facility+website&rft.atitle=Standard+Microscopy+Terminology&rft_id=http%3A%2F%2Fwww.charfac.umn.edu%2Fglossary%2Ff.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFocus+%28optics%29" class="Z3988"></span></span> </li> </ol></div></div> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol 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