It is a series starting from the first M645 released in 1975.
The characteristic is a classical appearance which clothed metal exterior as a leather sticker.
M645 1000 S/1976
The big difference is the shutter speed.
Maximum 1 / 500th of M645 and M645J.
As the name implies, the M645 1000S will be up to 1/1000 second.
In addition, these three models are fixed type which can not exchange film bags.