Late Bronica S2A in black with Bronica Zenzanon 80mm F2.4 and two black backs.
 
The Bronica S2, is a 6×6 focal plane SLR released by Bronica in 1965, is the successor of the Bronica S. From 1972 it was overshadowed by the Bronica EC, but improved revisions of the S2 continued to be marketed for a number of years before being officially discontinued in 1977.
The S2 included a number of minor changes from the S, but the main improvement was the switch to a removable helical focusing mount. This mount could focus lenses with focal lengths from 40mm to 200mm; longer lenses have their own helicoids (either separate or integrated) and can be mounted to the bayonet. The bellows accessory also uses the bayonet to mount onto the body. Mirror lock down feature is no longer available. The film back has also been improved; now with the capability to accept 220 roll film, the choice of 120 or 220 is selectable with a small dial on the film back.
The S2 uses a vertical-travelling cloth focal plane shutter. Shutter speeds are available from 1 to 1/1000s and B. Flash sync uses X and FP on an automatic PC terminal at a 1/40s sync speed. The shutter must be cocked before each shot by cranking the film winding lever. Many who used the system for the first time are often a bit too careful when using the film advance knob. One needs to advance the knob typically 3 to 4 complete rotations or multiple smaller rotations until it feels like it stops then rotate a bit more until you hear the shutter cock. This sounds is often very unnatural and feels like something broke.
Along with using 120 / 220 roll film, a instant peel-apart Polaroid back was also available for the S2. Film backs are removed from the camera by inserting a dark slide and pressing it firmly into the slot. As a safety feature, the shutter will not fire if the dark slide is not removed. Because all of the camera functions are fully mechanical, no battery is needed.
The standard lens for the S2 was a 75mm f/2.8 Nikkor P. The regular version of the camera uses chrome on the body, an alternate model called S2 Black was also available without the bright chrome. A similar version called Bronica C2was also available, with a non-removable integrated back.
The Bronica S2A was released in 1969 and is the successor of the S2. It specifications and outer appearance are nearly identical to those of the S2. The main difference is an improved film advance gear mechanism, reputed to result in fewer jams. The film advance and cocking dial has been changed and is smaller than the previous version.
 
Text from Camera-wiki.org