The Bronica SQ series is a line of 6x6 medium format SLR camera systems, introduced in 1980, with production of the last SQ-Ai model concluding in September 2003. The Bronica SQ, released in August 1980, replaced the Bronica EC as their 6x6 format camera. Similar to the earlier 6x4.5 ETR series, the SQ uses a leaf shutter based lens design, which is not compatible with older focal plane shutter cameras. Its lens system features a Seiko-manufactured electronic shutter with speeds from 8 seconds to 1/500 second, plus T mode, and includes a focusing helicoid built into each lens. A key feature of this leaf shutter system is flash synchronization at all speeds. The camera also incorporates an interchangeable back system that can use 120 or 220 film, with ISO speed dials on the backs that couple with metered finders. The SQ-A, released in 1982, added mirror lockup and a new viewfinder system supporting auto exposure. The SQ-Am, introduced in January 1983, was an integrated motor-drive-only version of the SQ-A. The SQ-Ai, announced at Photokina 1990, was an updated SQ-A with motor drive capability, OTF metering, and TTL automatic flash support. The SQ-B, made in 1996, is a simplified version of the SQ-A.