thumb|Binoviewer
A '''binoviewer''' is an optical device designed to enable binocular viewing through a single objective, primarily to reduce fatigue when peering down a single objective.
==Design== thumb|A binoviewer for an astronomical telescope.<ol> <li>Eyepiece</li><li>Compensation slide</li><li>Prism</li><li>Beam splitter</li><li>Body</li><li>Barlow lens</li></ol> In contrast to binoculars and stereo microscopes, which provide independent optical paths to each eye, both images in the binoviewer are produced by the same objective<ref name=Linssen/>{{rp|98}} and do not differ except for aberrations induced by the binoviewer itself. Because the eyes and brain still process the image binocularly, it provides a false stereoscopic view from a fundamentally monocular design.
A binoviewer consists of a beam splitter which splits the image provided by the objective into two identical (but fainter) copies,<ref name=Linssen/>{{rp|98}} and a system of prisms or mirrors that relay the images to a pair of identical eyepieces. The two eyepieces serve to provide greater viewing comfort.<ref name=Bradbury-68/>{{rp|196}}<ref name=Payne57>{{cite book |url=https://archive.org/details/microscopedesign0000payn/page/86/mode/2up |title=Microscope Design and Constructions |first=Bryan Oliver |last=Payne |date=1957 |publisher=Cooke, Troughton & Simms, Ltd. |location=York |edition=2nd |url-access=registration}}</ref>{{rp|87}}
The binoviewer was first popularized by a design credited to Francis Herbert Wenham around 1860.<ref name=Bradbury-68>{{cite book |url=https://archive.org/details/TheMicroscope-PastAndPresent/ |title=The Microscope: Past and Present |first=S. |last=Bradbury |date=1968 |publisher=Pergamon Press}}</ref>{{rp|197}}<ref name=nikonstereo1>{{cite web |url=http://www.microscopyu.com/articles/stereomicroscopy/stereointro.html |title=Introduction to Stereomicroscopy |first1=Paul E. |last1=Nothnagle |first2=William |last2=Chambers |first3=Michael W. |last3=Davidson |author3-link=Michael W. Davidson |publisher=Nikon |website=MicroscopyU |access-date=8 August 2025}}</ref><ref name=Linssen>{{cite book |url=https://archive.org/details/stereophotograph0000efli/ |title=Stereo-photography in Practice |first=E. F. |last=Linssen |date=1952 |publisher=The Fountain Press |location=London |url-access=registration}}</ref>{{rp|94}} The binoviewer was refined using roof prisms by Jentzsch and Siedentopf in the 1910s.<ref name=Belling>{{cite book |url=https://archive.org/details/useofmicroscope0000john/ |title=The Use of the Microscope |first=John |last=Belling |date=1930 |publisher=McGraw-Hill |url-access=registration}}</ref>{{rp|38}}{{rp|47}}
===Applications=== Binoviewers are a standard component of laboratory microscopes and are also used with optical telescopes, particularly in amateur astronomy.
Trinocular splitters are also used, where a camera is to be attached as well.
==References== {{reflist}}
Category:Optical devices Category:Microscope components
{{optics-stub}}