Twin-Lens Reflex (TLR) cameras are defined by having two lenses. One lens is used for taking images and the other is for viewing, focusing, and framing your photos. The lenses are synchronized and the same focal length to allow for proper framing and focusing.
Normally, the viewing lens redirects light upwards towards a waist level viewfinder and the lower lens exposes the film using a built-in leaf shutter. Because of the way this system works the image in the viewfinder is flipped horizontally, which can take some time to get used to. There are also slight differences in framing between the two lenses that can affect images at close focusing distances.
Most TLRs take 6x6cm images on 120 medium format roll film, although some could also use now-discontinued 220 film. Many companies made TLRs, including Yashica, Minolta, and Zeiss Ikon. The most famous TLR brand, though, is Rollei.
The Rolleicord and Rolleiflex cameras are the definitive TLR designs, with all others taking major inspiration from them. These cameras pair world-class build quality with legendary Carl Zeiss & Schneider-Kreuznach lenses to make an excellent, if expensive, camera.
TLRs are iconic ”old school” cameras, used as the primary camera of journalists and documentary photographers for decades before 35mm SLRs took over. Most people will recognize a TLR as an ”old camera” and many will be intrigued by its strange (by today’s standards) two-lens design.
DHW Fototechnik is still making Rolleiflex TLRs today in Germany.