I have seen adapters to use Mamiya medium format lenses on K-mount cameras listed on eBay by Kippon and Fotodiox. These two adapters both appear to be of good quality, well machined, etc. I have the Fotodiox adapter, and photos of this adapter are attached. Prices on the Fotodiox adapters seem to be significantly lower than for the Kippon adapters. Why I cannot say. Both adapters seem to perform identically in fitting medium format M645 Mamiya lenses to Pentax K-mount cameras. With either adapter, the camera can be used in only Manual or Aperture Priority modes because neither adapter provides the electronic connection to the camera that would be needed for other modes.
There are fairly complete lines of M645 lenses in both the original C configuration as well as the N configuration. These lenses tend to be quite similar except for improved coatings on the N line. Both the C and N lenses tend to be very well built with all-metal construction, and generally lighter and more compact than their Pentax 645 counterparts. They are pleasing to use from a tactile standpoint, and I have found them easy to focus, though the focussing rings turn opposite from the Pentax direction. With Mamiya, your turn the ring to the left for infinity and to the right for closeup shots. Prices tend to be quite competitive, particularly for the C line, and I have found no problems with flare with the C coatings. For the same price, of course, the N line is to be preferred.
I have acquired nine of these lenses--including 45mm, 55mm, 70mm LS, 80mm.1.9, 80mm macro, 145mm soft focus, 150mm, 210mm, and 300mm. Generally speaking, these lenses tend to be a little lower in price than the A version of the Pentax medium format lenses and sometimes one stop slower than their Pentax counterparts, which may be why they can be produced in lighter and less bulky configurations than the Pentax lenses. Mostly these lenses offer no particular advantages over their Pentax counterparts although there are a few standouts. I particularly like the uber-fast Mamiya 645 C 80mm f 1.9, said to be the fastest medium format lens ever produced. The 145mm soft focus lens is the best soft focus lens I have ever used; though the soft focus lenses are no longer much in vogue I still like playing around with them. At the long end, the 150mm and the 210mm are quite sharp and offer a lot of reach for the money for K-1, K-3 cameras. There are some super long lenses (500mm) as well as several zooms that I have not tried and cannot comment upon.
Overall, this exercise in adapting Mamiya medium format lenses to the K-mount cameras has not produced any startling results, though you certainly can get some quality glass for low prices. Corner performance should be excellent since on K-mount cameras you are using the sweetest part of the image circle. I should point out in closing that it is not possible to adapt these lenses to the Pentax 645 line of cameras owing to incompatible registry distances which would necessitate including corrective glass in the adapter, and so far as I am aware no such adapter has been built.
Originally posted by K1N8 
Post #2 by pepperberry farm
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