I have a Mamiya M645 SUPER medium format camera. I have had it for a while, probably about 8 years or so. Its in pretty good condition, and fully functional. One thing that I keep forgetting is the lens conversion factors between medium format and 35mm. I intuitively know what the 35mm lengths mean now so it is useful to be able to convert.
So a 645 medium format camera has a negative area of 56 x 41.5mm, which is 2.6 times the area of a (full-frame) 35mm at 36 x 24mm. This is a crop factor of 0.62075x. So the equivalent length are lower.
The chart of lengths is as follows:
|645 Lens||35mm Equivalent||645 Lens||35mm Equivalent|
The spread of lens I have now is good, from a standard equivalent 50mm, a 35mm equivalent, and a 28mm equivalent. The 35mm length is one of my favourites for photography, and it is also nice to have the wide angle. I would love a 90mm equivalent (150mm) for portrait work. I will keep an eye on eBay for one of the those.