cameras were known in some photographic discussions as 'the poor man's Nikon'. Periflex One unique brand of cameras was the Corfield Periflex made by K. G. Corfield Ltd in England. Three models were produced from 1957, all of which used a retractable periscope inserted into the light path for focussing through the single lens. Pressing the shutter release moved the spring-loaded periscope out of the film path before the focal-plane shutter operated Minolta Minolta's first SLR, the SR-2, was introduced to the export market in the same year (in fact, at the same Philadelphia show as the Canon and Nikon products) but had been on sale in Japan since August 1958. Lenses started with the designation 'Rokkor'. With the introduction of the SRT-101, the lenses added the designation of 'MC' for 'meter-coupled', and then later to 'MD' when the Minolta XD-11 was introduced with full-program mode. Minolta was taken over in 2003 by Konica, to form 'Konica-Minolta'. Konica-Minolta sold its imaging division to Sony in January 2006. Nikon F Nikon's 'F' model, introduced in April 1959 as the world's first system camera (if the commercially unsuccessful Praktina is not considered), became enormously successful and was the camera design that demonstrated the superiority of the SLR and of the Japanese camera manufacturers. This camera was the first SLR system that was adopted and used seriously by the general population of professional photographers, especially by those photographers covering the Vietnam War, and those news photographers utilizing motor-driven Nikon F's with 250-exposure backs to record the various launches of the space capsules in the Mercury, Gemini, and Apollo space programs, both in the 1960s. After the introduction of the Nikon F, the more expensive rangefinder cameras (those with focal plane shutters) became less attractive. It was a combination of design elements that made the Nikon F successful. It featured interchangeable prisms and focusing screens; the camera had a depth-of-field preview button; the mirror had lock-up capability; it featured a large bayonet mount and a large lens release button; a single-stroke ratcheted film advance lever; a titanium-foil focal plane shutter; various types of flash synchronization; a rapid rewind lever; and a fully removable back. it was a well-made, extremely durable camera, and adhered closely to the then current, successful design scheme of the Nikon rangefinder cameras. Instead of the M42 screw mount used by Pentax and other camera manufacturers, Nikon had introduced the three-claw