The single-lens reflex
) is a type of camera
that uses a movable mirror placed between the lens
and the film to project the image seen through the lens to a matte focusing
screen. Most SLRs use a roof pentaprism
to observe the image via an eyepiece, but there are also other finder arrangements, such as the waist-level finder or porro prisms
Large format SLR cameras were first built in the early years of the 20th century. The Ihagee Kine-Exakta was the first 35 mm SLR and it was truly influential. Further Exakta models, all with waist-level finders, were produced up to and during World War II. Another ancestor of the modern SLR camera was the Swiss-made Alpa, which was innovative, and proved influential for the later Japanese cameras. The first solution for an eye-level viewfinder was patented in Hungary during the war,—more precisely, on August 23, 1943, by Jenő Dulovits. The first 35mm camera that had one implemented was the Duflex, designed by Dulovits. This camera utilised a system of mirrors to provide a laterally correct, upright image in the eye-level viewfinder. The Duflex, which went into serial production in 1948, was also the world's first SLR with an instant-return (a.k.a. autoreturn) mirror.