The Bronica S2a 6×6 camera was made from about 1969 to 72. It was the successor of the S2. Having been given an improved film advance gear mechanism, resulting in fewer jams, usually the result of over enthusiastic film advancement.
This range of Bronica cameras had somewhat of a reputation for not being very sharp – even with the excellent Nikkor lens range that was provided.
It has been found that a number of things contributed to this problem:
The ground glass screen can be out of alignment and not allow sharp focus at the Infinity mark. Also to make matters worse, the foam under the screen deteriorates with age exacerbating the problem.
Film back inserts that would not seat properly.
Film roller problems with earlier backs which would allow the film to bow slightly. Later corrected by Bronica.
This all makes it sound unworthwhile bothering with these cameras which is far from the case: all it needs is a little care and attention. See this link for further information and corrective action. Link here. see below (as of 2014)
They have an excellent selection of Nikkor lenses, a large range of accessories and with the above problems sorted out, are capable of producing some fine images.
Further links of interest:
dirapon.be/bronica Lot of very good images about these cameras (French, but if you do not have : still worth a visit)
medfmt.8k.com/bronica This link is down as of 2014 I use the one below: