Twin-lens reflex camera
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.
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.
[4] A major step forward to mass marketing of the TLR came with the Rolleiflex in 1929, developed by Franke & Heidecke in Germany.
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.
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.
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.
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".
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.
Owing to the availability of medium-format cameras and the ease of image composition, the TLR was for many years also preferred by many portrait studios for static poses.
Extreme dark photographic filters like the opaque Wratten 87 can be used without problems, as they cover and thus darken only the taking lens.
Parallax compensation may be performed by the photographer in adjustment of the sight line while compensating for the framing change, or for highly repeatable 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.
Some TLRs like the Rolleiflex (a notable early example is the Voigtländer Superb of 1933[11]) also came with – more or less complex – devices to adjust parallax with focusing.
The image in the waist-level finder is reversed "left to right", which can make framing a photograph difficult, especially for an inexperienced user or with a moving subject.
Presently, the Chinese Seagull Camera is still in production along with Lomography's Lubitel, but in the past, many manufacturers made them.
[12] 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.
[13] 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 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 35 mm TLRs were made, the very expensive Contaflex TLR[14] being the most elaborate, with interchangeable lenses and removable backs.
Gemflex is a subminiature twin lens reflex camera made by Showa Optica Works (昭和光学精機) in occupied Japan in the 50s.
Japan made Gemflex, a twin lens reflex using 17.5 mm paper back roll film.
