between the lens and camera. Some even had image reversing optics. They also solved the RF camera's parallax error problem in macrophotography. Eventually, real SLRs were recognized as the simpler solution and supplanted RFs in the 1960s. The last reflex housing for a film camera, the Leica Visoflex III (West Germany; for Leica M4 series RFs), was discontinued in 1984. 1937 Gosudarstevennyi Optiko-Mekhanichesky Zavod (GOMZ) Sport (Спорт; Soviet Union): a 35 mm (not 135 type) SLR apparently prototyped in 1935. However, sources are uncertain or conflict upon the Sport's introduction date – a plurality say 1937. If it was sold in 1935, it would be the first 35 mm SLR. In any event, the Sport was not widely available and had no influence on later SLRs."Contact Sheet: Slighting the Exacta?" p. 94. Popular Photography, Volume 64 Number 10; October 2000. Lea, pp. 99–101Wade, Collector's Guide. p. 24 1940s 1947 Gamma Duflex (Hungary): first instant return mirror SLR, first metal focal-plane shutter SLR, first internal semi-automatic lens diaphragm SLR. Also had a mirror "prism" viewfinder, an intermediate step to a solid pentaprism. Reflex mirrors coupled to the shutter release had been spring actuated to rise automatically since the 19th century, but the viewfinder would remain blacked-out until the mirror was manually cocked back down. With an automatic, instant return mirror, the viewfinder blackout time might be as short as ⅛th second. The semi-auto diaphragm closed the lens diaphragm with shutter release, but it needed to be manually re-cocked open. The Duflex was very ambitious but very unreliable and Gamma's first and last production SLR. 1947 Rectaflex (Italy): first SLR camera equipped with a pentaprism for eye-level viewing. The first prototype of the Rectaflex was presented by Telemaco Corsi at the Milano Fair in April 1947. It was a wooden mock-up, with a mirror eye-level finder. This first prototype used a five-facet roof optic prism giving a left to right inverted image. For vertical pictures, the image was upside down, and that was a big drawback. This was corrected with a Goulier prism before the 1948 Milano Fair. 1948 Hasselblad 1600F (Sweden): first 2¼ medium format system SLR suitable for professional use. Took twelve exposures of 2¼×2¼ inch (6×6 cm) nominal frames (56×56 mm actual frames) on 120 film. Had modular design accepting interchangeable lenses, film magazines and folding waist level finder. The 1/1600 second corrugated stainless steel focal-plane shutter was unreliable