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 (the lens that takes the picture), while the other is used for the waist-level viewfinder system. 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 TLR's are fixed-focus models. Higher-end TLR's 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, since the image on the matte screen is reversed left-to-right. Mamiya's C-Series, introduced in the 60's, the C-3, C-2, C-33, C-22 and the Mamiya C330 and Mamiya C220 were some of the few TLR cameras to use interchangeable lenses. Rollei Rolleiflex model TLRs have an additional feature for the "sports finder" that allows precise focusing. 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 reveresed both top to bottom and left to right. TLR's are different from Single-lens-reflex cameras (SLR) in several respects. First, unlike most SLRs, TLRs provide a continuous image on the finder screen. The view does not black out during exposure. Additionally, models with leaf shutters rather than focal-plane shutters can synchronize with flash at higher speeds than can SLR's. However, because the photographer views through one lens but takes the photograph through another, parallax error makes the photograph different from the view on the screen. This difference is negligible when the subject is far away, but is critical for nearby subjects. For accuracy in tabletop photography, in which the subject might be within a foot (30 cm) of the camera, devices are available that move the camera upwards so that the taking lens goes to the exact position that the viewing lens occupied. A primary advantage of the TLR is its simplicity as compared to the more common single-lens reflex cameras. The SLR must employ some method of blocking light from reaching the film during focusing, either with a focal plane shutter (most common) or with the reflex mirror itself. Both methods add significant noise to the camera's operation. Most TLR's use a leaf shutter in the lens. The only mechanical noise during exposure is from the shutter leaves opening and closing. The typical TLR is medium format, using 120 roll film with square 6 x 6 cm images. Presently, the Chinese Seagull and the German Rollei are in production, but in the past, many manufacturers made them. 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 TLR's had interchangeable lenses, allowing focal lengths from 55mm (wide angle) to 250mm (telephoto) to be used. There were smaller TLR models, using 127 roll film with square 4 x 4 cm images, most famous the "Baby" Rolleiflex and the Yashica 44. The TLR style was also popular in the 1950's for inexpensive fixed focus cameras such as the Kodak Duaflex and Argus 75. The smallest TLR camera is the Swiss made Tessina, using performated 35mm film forming images of 14x21 mm. From Wikipedia

The typical TLR is medium format, using 120 roll film with square 6 x 6 cm images. Presently, the Chinese Seagull and the German Rollei are in production, but in the past, many manufacturers made them. 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 TLR's had interchangeable lenses, allowing focal lengths from 55mm (wide angle) to 250mm (telephoto) to be used.

There were smaller TLR models, using 127 roll film with square 4 x 4 cm images, most famous the "Baby" Rolleiflex and the Yashica 44. The TLR style was also popular in the 1950's for inexpensive fixed focus cameras such as the Kodak Duaflex and Argus 75.

The smallest TLR camera is the Swiss made Tessina, using performated 35mm film forming images of 14x21 mm.

From Wikipedia