Mamiya was founded in 1940. They soon started producing 6x6 cameras and did so throughout the 40s and 50s. Their first PP SLR was market ready in 1961 with the name Prismat. However, according to http://herron.50megs.com/prismat.htm ,
they had a prototype ready in 1952 called Prismflex, and another called Pentaflex in 1955. (Now, that is very strange, as Tokiwa Seiki produced a Pentaflex, too, in 1955 with central shutter and looking very different from what the picture or drawing
of the Mamiya shows.) Why it took so long to produce it for the market, especially when others already were there, is hard to say. Anyway, Mamiya produced different Prismat models until 1966, when the new TL series came with TTL metering. From 1968 the DTL
took over. This was the first camera to give the user the choice between average and spot metering. This series was probably their most popular one. Then followed the XTL, X-1000, MSX, DSX, NP 1000 and Z-series. Mamiya changed mounts several times, making
it difficult to bring old lenses to new cameras. From the first Prismat NP mount via a breach lock for the Prismat PH and CPH to the M42 on the CP in '64, still M42 on TL, DTL, MSX and DSX, then a new mount on the NC 1000 line, and finally another new mount
on the Z-series. In addition to this, Mamiya produced some beginners PP SLR with fixed lenses from 1962, the so-called Family, then the 528 TL in '68 and the 528 SL in '75.
Miyata was innovative but was not paid back. The sales were not as
expected, and when their worldwide distributor Osawa went down in 1984, the whole Miyata company went with them. They were reorganised the year after but gave up 35 mm cameras to fully concentrate on medium format cameras. So, it was back to start. Since
then, they have reorganised again, and the new company, now controlled by Danish Phase One, is still producing digital medium format cameras under the name Mamiya Leaf.