Editing Twin-lens reflex camera (section)

==History==
[[Image:Twin Lens Camera.png|right|thumb|Sketch of an early-20th-century twin-lens reflex camera]] 
In traditional cameras, the photographer first viewed the image on a screen of ground glass in the same place that a photographic plate would be placed. After adjusting the camera and closing the objective aperture the ground glass screen was swapped for the photographic plate, and finally the picture could be taken. (Some cameras used this layout as late as the 1960s, for example the Koni-Omegaflex.<ref>
{{cite web
 | title= Koni-Omegaflex
 | website= www.tlr-cameras.com
 | url= http://www.tlr-cameras.com/Japanese/slides/Koni-Omegaflex.html
 | access-date= 10 April 2018
}}
</ref>)
With the addition of a second lens and a permanent piece of ground glass, this made it possible for a photographer to snap a picture immediately after focusing the image instead of having to remove and replace the ground glass screen every shot.<ref name=Holmes1978>
{{cite book
 | last1= Holmes
 | first1= Edward
 | title= An Age Of Cameras
 | date= 1978
 | isbn= 978-0-8524-2346-2
 | page= 11
 | publisher= Fountain Press
 | url= https://books.google.com/books?id=wtY4AQAAIAAJ&q=ground+glass
 | access-date= 27 June 2015
}}
</ref>
This advantage of course applies to SLR cameras as well, but early SLR cameras caused delays and inconvenience due to moving the mirror needed for viewfinding out of the optical path to the photographic plate. When this process was automated, the movement of the mirror could cause shake in the camera and blur the image.
Using a mirror to allow viewing from above also enabled the camera to be held much more steadily against the body than a camera held with the hands only.

The London Stereoscopic Co's "Carlton" model, dating from 1885, is claimed to be the first off-the-shelf TLR camera.<ref>
{{cite web
 | title= WWW.TLR-CAMERAS.COM/History
 | website= www.tlr-cameras.com
 | url= http://www.tlr-cameras.com/history.htm
 | access-date= 10 April 2018
}}
</ref>
A major step forward to mass marketing of the TLR came with the [[Rolleiflex]] in 1929, developed by Franke & Heidecke in Germany. The Rolleiflex was widely imitated and most mass-market TLR cameras owe much to its design. It is said that Reinhold Heidecke had the inspiration for the Rollei TLRs while undertaking photography of enemy lines from the German trenches in 1916, when a periscopic approach to focusing and taking photos radically reduced the risk to the photographer from sniper fire.<ref>"Complete Collector's Guide to the Rollei TLR, Ian Parker, Hove Photo Books, Jersey, 1993</ref>

TLRs are still manufactured in Germany by DHW Fototechnik, the successor of [[Rollei|Franke & Heidecke]], in three versions.<ref>{{cite web|url=http://www.popphoto.com/gear/2012/09/rolleiflex-unveils-new-fx-n-tlr-film-hy6-mod2-medium-format-cameras-electronic-shutter|title=DHW Fototechnik unveils new version of the classic Rolleiflex TLR camera|date=17 January 2019}}</ref>