Editing Binoculars (section)

===== Porro =====
[[File:Double Porro prism.svg|thumb|Double Porro prism design]]

''[[Porro prism]] binoculars'' are named after Ignazio Porro, who patented this image erecting system in 1854. The later refinement by Ernst Abbe and his cooperation with glass scientist [[Otto Schott]], who managed to produce a better type of Crown glass in 1888, and instrument maker [[Carl Zeiss]] resulted in 1894 in the commercial introduction of improved 'modern' Porro prism binoculars by the [[Carl Zeiss AG|Carl Zeiss company]].<ref name="Europa"/><ref>[https://www.allbinos.com/index.php?art=187 History of 7x50 binoculars from Jena]</ref> Binoculars of this type use a pair of Porro prisms in a Z-shaped configuration to erect the image. This results in wide binoculars, with objective lenses that are well separated and offset from the [[eyepiece]]s, giving a better sensation of depth. Porro prism designs have the added benefit of [[Folded optics|folding]] the [[optical path]] so that the physical length of the binoculars is less than the [[focal length]] of the objective. Porro prism binoculars were made in such a way to erect an image in a relatively small space, thus binoculars using [[Prism (optics)|prism]]s started in this way.

Porro prisms require typically within 10 [[Minute and second of arc|arcminutes]] ({{sfrac|1|6}} of 1 [[Degree (angle)|degree]]) tolerances for alignment of their optical elements ([[collimation#Collimation and decollimation|collimation]]) at the factory. Sometimes Porro prisms binoculars need their prisms set to be re-aligned to bring them into collimation.<ref name="books.google.com">{{cite book|url=https://books.google.com/books?id=piwP9HXtpvUC&q=%22porro+prism%22+binoculars+produce+brighter+image+than+%22roof+prism%22&pg=PA34|title='' Astronomy Hacks'', chapter 1, page 34|date=2005-06-24|access-date=2009-11-03|isbn=9780596100605|last1=Thompson|first1=Robert Bruce|last2=Thompson|first2=Barbara Fritchman|publisher="O'Reilly Media, Inc." |archive-date=2022-04-19|archive-url=https://web.archive.org/web/20220419130538/https://books.google.com/books?id=piwP9HXtpvUC&q=%22porro+prism%22+binoculars+produce+brighter+image+than+%22roof+prism%22&pg=PA34|url-status=live}}</ref> Good-quality Porro prism design binoculars often feature about {{convert|1.5|mm|in|2}} deep grooves or notches ground across the width of the [[hypotenuse]] face center of the prisms, to eliminate image quality reducing abaxial non-image-forming reflections.<ref>{{Cite web |url=https://nimax-img.de/Produktdownloads/44543_3_Leseprobe.pdf |title=Binocular Optics and Mechanics Chapter from Binocular Astronomy by Stephen Tonkin, page 14 |access-date=2022-05-23 |archive-date=2022-08-18 |archive-url=https://web.archive.org/web/20220818165600/https://nimax-img.de/Produktdownloads/44543_3_Leseprobe.pdf |url-status=live }}</ref> Porro prism binoculars can offer good optical performance with relatively little manufacturing effort and as human eyes are ergonomically limited by their [[#Interpupillary_distance|interpupillary distance]] the offset and separation of big (60<sup>+</sup> mm wide) diameter objective lenses and the eyepieces becomes a practical advantage in a stereoscopic optical product.

In the early 2020s, the commercial market share of Porro prism-type binoculars had become the second most numerous compared to other prism-type optical designs.<ref>{{Cite web |url=https://www.optics-trade.eu/en/binoculars.html |title=Binoculars dealer summary, showing 239 listed Porro prism designs and 777 binoculars that use other optical designs in May 2022 |access-date=2022-05-24 |archive-date=2015-11-01 |archive-url=https://web.archive.org/web/20151101110203/http://www.optics-trade.eu/en/binoculars.html |url-status=live }}</ref><!--Binoculars dealer summary, showing 239 listed Porro prism designs and 777 binoculars that use other optical designs in May 2022-->

There are alternative Porro prism-based systems available that find application in binoculars on a small scale, like the  [[Perger prism]] that offers a significantly reduced axial offset compared to traditional Porro prism designs .<ref>{{Cite web |url=https://worldwide.espacenet.com/patent/search/family/045444542/publication/EP2463692A1?q=pn%3DEP2463692A1 |title=European Patent EP2463692A1 ''Prism'' |access-date=2022-05-26 |archive-date=2022-05-26 |archive-url=https://web.archive.org/web/20220526083037/https://worldwide.espacenet.com/patent/search/family/045444542/publication/EP2463692A1?q=pn%3DEP2463692A1 |url-status=live }}</ref><ref>{{Cite web |url=https://www.optics-trade.eu/en/binoculars.html |title=Binoculars dealer summary, showing 10 listed Porro-Perger prism designs and 1,006 binoculars that use other optical designs in May 2022 |access-date=2022-05-24 |archive-date=2015-11-01 |archive-url=https://web.archive.org/web/20151101110203/http://www.optics-trade.eu/en/binoculars.html |url-status=live }}</ref><!--Binoculars dealer summary, showing 10 listed Porro-Perger prism designs and 1,006 binoculars that use other optical designs in May 2022-->