Editing Binoculars (section)

== Optical design evolution ==

=== Galilean ===
[[File:Binoculars (AM 2004.5.5-3).jpg|thumb|WW1 era [[Galilean telescope|Galilean]] type binoculars]]
Almost from the invention of the telescope in the 17th century the advantages of mounting two of them side by side for binocular vision seems to have been explored.<ref name="Europa">{{cite web|url=http://www.europa.com/~telscope/binohist.txt |title=Europa.com — The Early History of the Binocular |archiveurl=https://web.archive.org/web/20110613204340/http://www.europa.com/~telscope/binohist.txt |archivedate=2011-06-13 }}</ref> Most early binoculars used [[Galilean telescope|Galilean optics]]; that is, they used a [[convex lens|convex]] [[objective (optics)|objective]] and a [[concave lens|concave]] [[eyepiece|eyepiece lens]]. The Galilean design has the advantage of presenting an [[erect image]] but has a narrow field of view and is not capable of very high magnification. This type of construction is still used in very cheap models and in [[opera glasses]] or theater glasses. The Galilean design is also used in low magnification binocular surgical and jewelers' [[loupe]]s because they can be very short and produce  an upright image without extra or unusual erecting optics, reducing expense and overall weight. They also have large exit pupils, making centering less critical, and the narrow field of view works well in those applications.<ref>{{cite book |author=Mark E. Wilkinson |url=https://books.google.com/books?id=ngGzZe-5PBYC&pg=PA65 |page=65 |title=Essential Optics Review for the Boards |isbn=9780976968917 |publisher=F.E.P. International |date=2006 |access-date=2016-10-10 |archive-date=2016-12-27 |archive-url=https://web.archive.org/web/20161227131105/https://books.google.com/books?id=ngGzZe-5PBYC&pg=PA65 |url-status=live }}</ref> These are typically mounted on an eyeglass frame or custom-fit onto eyeglasses.

=== Keplerian ===
An improved image and higher magnification are achieved in binoculars employing [[Keplerian Telescope|Keplerian optics]], where the image formed by the objective lens is viewed through a positive eyepiece lens (ocular).
Since the Keplerian configuration produces an inverted image, different methods are used to turn the image the right way up.

==== Erecting lenses ====

In aprismatic binoculars with Keplerian optics (which were sometimes called "twin telescopes"), each tube has one or two additional lenses ([[relay lens]]) between the objective and the eyepiece. These lenses are used to erect the image. The binoculars with erecting lenses had a serious disadvantage: they are too long. Such binoculars were popular in the 1800s (for example, [[G. & S. Merz]] models). The Keplerian "twin telescopes" binoculars were optically and mechanically hard to manufacture, but it took until the 1890s to supersede them with better prism-based technology.<ref>{{cite conference |url=http://fp.optics.arizona.edu/antiques/History%20of%20Telescopes%20and%20Binoculars%20-%20SPIE.pdf |first1=John E. |last1=Greivenkamp |first2=David L. |last2=Steed |title=The History of Telescopes and Binoculars: An Engineering Perspective |book-title=Proc. SPIE 8129, Novel Optical Systems Design and Optimization XIV, 812902 |editor1=R. John Koshel |editor2=G. Groot Gregory |date=10 September 2011 |issn=0277-786X |doi=10.1117/12.904614 |s2cid=123495486 |archiveurl=https://web.archive.org/web/20141129083421/http://fp.optics.arizona.edu/antiques/History%20of%20Telescopes%20and%20Binoculars%20-%20SPIE.pdf |archivedate=2014-11-29 |url-status=live}}</ref><ref>{{Cite web |url=https://hinode-bino-guide.com/how-porro-prism-binoculars-work/ |title=How Porro Prism Binoculars Work |access-date=2022-10-08 |archive-date=2022-10-08 |archive-url=https://web.archive.org/web/20221008150334/https://hinode-bino-guide.com/how-porro-prism-binoculars-work/ |url-status=live }}</ref>

==== Prism ====
Optical [[Prism (optics)|prism]]s added to the design enabled the display of the image the right way up without needing as many lenses, and decreasing the overall length of the instrument, typically using [[Porro prism]] or [[roof prism]] systems.<ref>Michael D. Reynolds, Mike D. Reynolds, Binocular Stargazing, Stackpole Books – 2005, page 8</ref><ref>{{Cite web |url=https://www.opticscentral.com.au/blog/binocular-prisms/ |title=Binocular prisms – why are they so weird and different? Bill Stent, October 21, 2019 |date=21 October 2019 |access-date=May 29, 2022 |archive-date=March 16, 2022 |archive-url=https://web.archive.org/web/20220316033523/https://www.opticscentral.com.au/blog/binocular-prisms/ |url-status=live }}</ref> The Italian inventor of optical instruments [[Ignazio Porro]] worked during the 1860s with Hofmann in Paris to produce monoculars using the same prism configuration used in modern Porro prism binoculars. At the 1873 Vienna Trade Fair German optical designer and scientist [[Ernst Abbe]] displayed a prism telescope with two cemented Porro prisms. The optical solutions of Porro and Abbe were theoretically sound, but the employed prism systems failed in practice primarily due to insufficient glass quality.<ref>{{cite conference |url=http://fp.optics.arizona.edu/antiques/History%20of%20Telescopes%20and%20Binoculars%20-%20SPIE.pdf |first1=John E. |last1=Greivenkamp |first2=David L. |last2=Steed |title=The History of Telescopes and Binoculars: An Engineering Perspective |book-title=Proc. SPIE 8129, Novel Optical Systems Design and Optimization XIV, 812902 |editor1=R. John Koshel |editor2=G. Groot Gregory |date=10 September 2011 |issn=0277-786X |doi=10.1117/12.904614 |s2cid=123495486 |archiveurl=https://web.archive.org/web/20141129083421/http://fp.optics.arizona.edu/antiques/History%20of%20Telescopes%20and%20Binoculars%20-%20SPIE.pdf |archivedate=2014-11-29 |url-status=live}}</ref><ref name="Europa" />

===== 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-->

=====Roof=====
[[File:Schmidt-Pechan prism.svg|thumb|upright|Schmidt–Pechan "roof" prism design]]
[[File:Abbe-König prism.svg|thumb|Abbe–Koenig "roof" prism design|left]]

''[[Roof prism]] binoculars'' may have appeared as early as the 1870s in a design by Achille Victor Emile Daubresse.<ref name="google">{{cite web |url=http://groups.google.co.ke/group/sci.astro.amateur/tree/browse_frm/month/2002-08/5a0a50e6887feb69?rnum=71&_done=%2Fgroup%2Fsci.astro.amateur%2Fbrowse_frm%2Fmonth%2F2002-08%3F |title=groups.google.co.ke |access-date=2009-11-03 |archive-date=2010-07-30 |archive-url=https://web.archive.org/web/20100730175821/http://groups.google.co.ke/group/sci.astro.amateur/tree/browse_frm/month/2002-08/5a0a50e6887feb69?rnum=71&_done=%2Fgroup%2Fsci.astro.amateur%2Fbrowse_frm%2Fmonth%2F2002-08%3F |url-status=live }}</ref><ref name="PhotoDigital">{{Cite web |url=http://www.photodigital.net/lists/rec.photo.equipment.misc/4/0455.html |title=photodigital.net — rec.photo.equipment.misc Discussion: Achille Victor Emile Daubresse, forgotten prism inventor |access-date=2006-11-26 |archive-date=2010-07-31 |archive-url=https://web.archive.org/web/20100731095955/http://www.photodigital.net/lists/rec.photo.equipment.misc/4/0455.html |url-status=live }}</ref> In 1897 Moritz Hensoldt began marketing [[pentaprism]] based roof prism binoculars.<ref>{{cite conference |url=http://fp.optics.arizona.edu/antiques/History%20of%20Telescopes%20and%20Binoculars%20-%20SPIE.pdf |first1=John E. |last1=Greivenkamp |first2=David L. |last2=Steed |title=The History of Telescopes and Binoculars: An Engineering Perspective |book-title=Proc. SPIE 8129, Novel Optical Systems Design and Optimization XIV, 812902 |editor1=R. John Koshel |editor2=G. Groot Gregory |date=10 September 2011 |issn=0277-786X |doi=10.1117/12.904614 |s2cid=123495486 |archiveurl=https://web.archive.org/web/20141129083421/http://fp.optics.arizona.edu/antiques/History%20of%20Telescopes%20and%20Binoculars%20-%20SPIE.pdf |archivedate=2014-11-29 |url-status=live}}</ref>

Most roof prism binoculars use either the [[Schmidt–Pechan prism]] (invented in 1899) or the [[Abbe–Koenig prism]] (named after [[Ernst Karl Abbe]] and [[Albert König (optician)|Albert König]] and patented by Carl Zeiss in 1905) designs to erect the image and fold the optical path. They have objective lenses that are approximately in a line with the eyepieces.<ref name=sinnott />

Binoculars with roof prisms have been in use to a large extent since the second half of the 20th century. Roof prism designs result in objective lenses that are almost or totally in line with the eyepieces, creating an instrument that is narrower and more compact than Porro prisms and lighter. There is also a difference in image brightness. Porro prism and Abbe–Koenig roof-prism binoculars will inherently produce a brighter image than Schmidt–Pechan roof prism binoculars of the same magnification, objective size, and optical quality, because the Schmidt-Pechan roof-prism design employs mirror-coated surfaces that [[Schmidt–Pechan prism#Reflection losses|reduce light transmission]].

In roof prism designs, optically relevant prism angles must be correct within 2 [[arcsecond]]s ({{sfrac|1|1,800}} of 1 degree) to avoid seeing an obstructive double image. Maintaining such tight production tolerances for the alignment of their optical elements by laser or interference (collimation) at an affordable price point is challenging. To avoid the need for later re-collimation, the prisms are generally aligned at the factory and then permanently fixed to a metal plate.<ref name=hacks>{{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 |pages=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> These complicating production requirements make high-quality roof prism binoculars more costly to produce than Porro prism binoculars of equivalent optical quality and until [[phase correction coating]]s were invented in 1988 Porro prism binoculars optically offered superior resolution and contrast to [[Roof prism#Phase correction|non-phase corrected roof prism]] binoculars.<ref name=sinnott>{{cite web |url=https://skyandtelescope.org/astronomy-resources/astronomy-questions-answers/why-do-the-best-roof-prism-binoculars-need-a-phase-correction-coating/ |title=Why do the best roof-prism binoculars need a phase-correction coating? |author=Roger W. Sinnott |date=July 24, 2006 |work=Sky and Telescope |access-date=2022-07-20 |archive-date=2022-06-04 |archive-url=https://web.archive.org/web/20220604133953/https://skyandtelescope.org/astronomy-resources/astronomy-questions-answers/why-do-the-best-roof-prism-binoculars-need-a-phase-correction-coating/ |url-status=live }}</ref><ref name=hacks /><ref>{{cite book |url=https://nimax-img.de/Produktdownloads/44543_3_Leseprobe.pdf |chapter=Binocular Optics and Mechanics |title=Binocular Astronomy |author=Stephen Tonkin |isbn=978-1-4614-7466-1 |date=2014 |publisher=Springer |access-date=2022-07-20 |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><ref>{{cite web |url=https://www.ronspomeroutdoors.com/blog/porro-prism-binocular-best-buy |title=Porro Prism Binocular a Best Buy |author=Ron Spomer |access-date=2022-07-20 |archive-date=2020-11-12 |archive-url=https://web.archive.org/web/20201112011914/https://www.ronspomeroutdoors.com/blog/porro-prism-binocular-best-buy/ |url-status=live }}</ref>

In the early 2020s, the commercial offering of Schmidt-Pechan designs exceeds the Abbe-Koenig design offerings and had become the dominant optical design compared to other prism-type designs.<ref>{{Cite web |url=https://www.optics-trade.eu/en/binoculars.html |title=Binoculars dealer offerings, showing Schmidt-Pechan designs exceed the Abbe-Koenig designs by more than 13 times 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 offerings, showing Schmidt-Pechan designs exceed the Abbe-Koenig designs by more than 13 times in May 2022-->

Alternative roof prism-based designs like the [[Uppendahl prism]] system composed of three prisms cemented together were and are commercially offered on a small scale.<ref>{{Cite web |url=https://www.flickr.com/photos/binocwpg/8103359604/in/album-72157632281149716/ |title=Image of a Uppendahl prism system used in Leitz Wetzlar, Trinovid 7×42B binoculars. The first Trinovid series featuring a Uppendahl prism system was made until 1990. |date=18 October 2012 |access-date=2022-07-21 |archive-date=2022-07-21 |archive-url=https://web.archive.org/web/20220721181629/https://www.flickr.com/photos/binocwpg/8103359604/in/album-72157632281149716/ |url-status=live }}</ref><!--Image of a Uppendahl prism system used in Leitz Wetzlar, Trinovid 7×42B binoculars. The first Trinovid series featuring a Uppendahl prism system was discontinued in 1990.--><ref name="auto">{{Cite web |url=https://www.houseofoutdoor.com/wp-content/uploads/2020/02/Leica-kijker-test-dd-29-febr-2020.pdf |title=PROPERTIES AND PERFORMANCE OF THE NEW LEICA TRINOVID 7X35B (=HERE NAMED RETROVID) COMPARED WITH OLDER LEITZ-LEICA TRINOVIDS AND WITH BINOCULARS FROM BECK, FOTON AND THE NEW KOWA 6,5X32. February 2020 by Dr. Gijs van Ginkel |access-date=2022-09-10 |archive-date=2022-11-15 |archive-url=https://web.archive.org/web/20221115202450/https://www.houseofoutdoor.com/wp-content/uploads/2020/02/Leica-kijker-test-dd-29-febr-2020.pdf |url-status=live }}</ref>