A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens" (the lens that takes the picture), while the other is used for the viewfinder system, which is usually viewed from above at waist level. In addition to the objective, the viewfinder consists of a 45-degree mirror (the reason for the word reflex in the name), a matte focusing screen at the top of the camera, and a pop-up hood surrounding it. The two objectives are connected, so that the focus shown on the focusing screen will be exactly the same as on the film. However, many inexpensive TLRs are fixed-focus models. Most TLRs use leaf shutters with shutter speeds up to 1/500th sec with a B setting.
For practical purposes, all TLRs are film cameras, most often using 120 film, although there are many examples which used other formats. No general-purpose digital TLRs exist, since their heyday ended long prior to the digital era. The main exception is the collector-oriented Rollei Mini-Digi, introduced as a rather expensive "toy" in 2004.[1]
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Double-lens cameras seem first to have been developed around 1870, when someone realised that having a second lens alongside the taking lens meant that one could focus without having to keep swapping a ground glass screen for the plate afterwards, making the time delay in actually taking the shot rather less.[2] This sort of approach was still used as late as the 1960s, as the monstrous Koni-Omegaflex[3] testifies.
The TLR as such was an evolution using a reflex mirror to allow viewing from above, allowing the camera to be held much more steadily if handheld. The same principle of course applied to the SLR, but early SLRs caused delays and inconvenience through the need to move the mirror out of the focal plane to allow light to the plate behind it. When this process was automated, the movement of the mirror could cause shake in the camera and blur the shot. The London Stereoscopic Co's "Carlton" model is claimed to have been the first off-the-shelf TLR, dating from 1885.[4]
The major step forward to mass marketing of the TLR came with the Rolleiflex in 1929. The Rolleiflex was widely imitated and copied and most mass-market TLRs owe much to its design.
Higher-end TLRs may have a pop-up magnifying glass to assist the user in focusing the camera. In addition, many have a "sports finder" consisting of a square hole punched in the back of the pop-up hood, and a knock-out in the front. Photographers can sight through these instead of using the matte screen. This is especially useful in tracking moving subjects such as animals or race cars, since the image on the matte screen is reversed left-to-right. It is nearly impossible to accurately judge composition with such an arrangement, however.
Mamiya's C-Series, introduced in the 1960s, the C-3, C-2, C-33, C-22 and the Mamiya C330 and Mamiya C220 along with their predecessor the Mamiyaflex,[5] are the main conventional TLR cameras to feature truly interchangeable lenses.[6] The Mamiya TLRs also employ bellows focusing, making extreme closeups possible.
Many TLRs used front and back cut-outs in the hinged top hood to provide a quick-action finder for sports and action photography. Late model Rollei Rolleiflex TLRs introduced the widely-copied additional feature of a second-mirror "sports finder". When the hinged front hood knock-out is moved to the sports finder position a secondary mirror swings down over the view screen to reflect the image to a secondary magnifier on the back of the hood, just below the direct view cutout. This permits precise focusing while using the sports finder feature. The magnified central image is reversed both top-to-bottom and left-to-right. This feature made Rolleis the leading choice for press photographers during the 1940s to 1960s.[7]
The typical TLR is medium format, using 120 roll film with square 6×6 cm images. Presently, the Chinese Seagull Camera is still in production along with Lomography's Lubitel, but in the past, many manufacturers made them. The Ciro-flex produced by Ciro Cameras Inc. rose dramatically in popularity due in large part to the inability to obtain the German Rollei TLRs during World War II. The Ciro-flex was widely accessible, inexpensive, and produced high quality images.[10] Models with the Mamiya, Minolta and Yashica brands are common on the used-camera market, and many other companies made TLRs that are now classics. The Mamiya C series TLRs had interchangeable lenses, allowing focal lengths from 55mm (wide angle) to 250mm (telephoto) to be used. The bellows focusing of these models also allowed extreme closeups to be taken, something difficult or impossible with most TLRs. The simple, sturdy construction of many TLRs means they have tended to endure the years well. Many low-end cameras used cheap shutters however, and the slow speeds on these often stick or are inaccurate.
There were smaller TLR models, using 127 roll film with square 4×4 cm images, most famous the "Baby" Rolleiflex and the Yashica 44. The TLR design was also popular in the 1950s for inexpensive fixed focus cameras such as the Kodak Duaflex and Argus 75. Though most used medium format film, a few 35mm TLRs were made, the Contaflex TLR being the most elaborate, with interchangeable lenses and removable backs.
The smallest general-use TLR camera is the Swiss-made Tessina, using perforated 35mm film forming images of 14×21 mm. It has been argued that the "business end" of the Olympus Gastro Camera[11] is technically the smallest actual TLR device.