automatic diaphragm release on Meyer Primotar E 3,5/50 1956 Zeiss Ikon Contaflex III (West Germany): first high-quality, interchangeable lens attachments, leaf shutter 35 mm pentaprism SLR with built-in selenium exposure meter. Was improved Contaflex I (see above) with redesigned Carl Zeiss unit-focusing Tessar lens,Small and Barringer, pp. 50–52 its front element can be removed and replaced with a set of Pro-Tessar lenses. 1956 VEB Kamerawerkstätten, Dresden-Niedersedlitz PRAKTICA FX 2 worlds first 35mm SLR with internal automatic diaphragm release for Meyer Primotar E 3,5/50 1957 Asahi Pentax (Japan; called Sears Tower 26 in USA): first SLR with right-handed rapid-wind thumb lever, first fold-out film rewind crank, first microprism focusing aid. First Asahi SLR with M42 screw mount. Established the "modern" control layout of the 35 mm SLR. Well-integrated focal-plane shutter, instant return mirror and pentaprism design.Matanle, p. 118 1957 Hasselblad 500C (Sweden): replaced the Hasselblad 1600F/1000F's (see above) problematic focal-plane shutter with reliable interlens Synchro-Compur leaf shutters and made the 2¼ medium format SLR the dominant professional studio camera by the late 1950s. Well-integrated, durable and reliable design without instant return mirror, but with excellent auto-diaphragm interchangeable lenses and large accessory system.Matanle, pp. 221–222 1958 Zunow SLR (Japan): first japanese internal auto-diaphragm (Zunow-matic Diaphragm System) 35 mm SLR and lenses. Well-integrated focal-plane shutter, instant return mirror, pentaprism and auto-diaphragm design with excellent lenses and good accessory system. Stopping down (closing) the lens aperture (iris) to prepare for exposure transmits less light to the mirror and the viewfinder may become very dim – perhaps even too dark to see the image. Auto-diaphragms coupled to the shutter release that automatically stop down when the mirror swings up and reopen when the mirror comes down provides almost continuous fully open aperture viewing. Auto-diaphragm lenses and instant return mirror, focal-plane shutter SLRs require precise camera-to-lens linkage, but can choreograph the entire shutter-button release, close lens, raise mirror, open shutter, close shutter, lower mirror, open lens exposure sequence in as little as ⅛th second. Originally, these were mechanical spring/gear/lever systems energized concurrent with manually winding the film, but modern systems are electronically timed and operated by an electromagnet. The financially weak Zunow company was unable to capitalize on its design; few examples of the camera (and much fewer of the wide and tele lenses for it) were produced before the company switched back to lenses for other companies' cameras. Zunow went bankrupt in 1961. Note, the