Twin-lens reflex

Twin-lens reflex cameras used a pair of nearly identical lenses, one to form the image and one as a viewfinder. The lenses were arranged with the viewing lens immediately above the taking lens. The viewing lens projects an image onto a viewing screen which can be seen from above. Some manufacturers such as Mamiya also provided a reflex head to attach to the viewing screen to allow the camera to be held to the eye when in use. The advantage of a TLR was that it could be easily focussed using the viewing screen and that under most circumstances the view seen in the viewing screen was identical to that recorded on film. At close distances however, parallax errors were encountered and some cameras also included an indicator to show what part of the composition would be excluded. Some TLR had interchangeable lenses but as these had to be paired lenses they were relatively heavy and did not provide the range of focal lengths that the SLR could support. Most TLRs used 120 or 220 film; some used the smaller 127 film. 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 s utter 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 TLR cameras exist, since the heyday of TLR cameras ended long before the era of digital cameras. The main exception is the collector-oriented Rollei Mini-Digi, introduced as a rather expensive "toy" in 2004. Double-lens cameras were first developed around 1870, due to the realization that having a second lens alongside the taking lens would mean that one could focus without having to keep swapping the ground glass screen for the plate, reducing the time required for taking a picture.[2] This sort of approach was still used as late as the 1960s, as the monstrous Koni-Omegaflex[3] testifies. The TLR camera was thus an evolution. Using a reflex mirror to allow viewing from above also enabled the camera to be held much more steadily than if it were to be held in the hand. The same principle of course applied to SLR cameras, but early SLR cameras caused delays and inconvenience through the need to move the mirror out of the focal plane to allow light to pass to the plate behind it. When this process was automated, the movement of the mirror could cause shake in the camera and blur the image. The London Stereoscopic Co's "Carlton" model is claimed to have been the first off-the-shelf TLR camera, 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 TLR cameras owe much to its design. TLRs are still manufactured in Germany by DHW Fototechnik, the successor of Franke & Heidecke in three versions.