Hello all, I thought this might be of interest to someone. 
Before I dived into medium format and began collecting a few lenses for my Mamiya ADF body, I looked into whether an adapter was available to convert the Pentax 645 glass to the Mamiya 645 mount, as my background is in Pentax and I'm reasonably familiar with the lenses. A lot of people had been asking the same question on forums for years, with the 35mm tending to be raised in conversation the most, due to reportedly being considered superior to the Mamiya in image quality and being a somewhat affordable wide-angle lens. Despite the interest, the answer was No, there is not an adapter.
So I looked into it a bit further and adapted a lens anyway. I purchased a good Pentax A 35mm, stripped the bayonet mount off it and machined up an adapting plate, including a bayonet. Overall, I'm happy that the thing actually works, as I completely bodged a Mk.I version of my adapter, but the Mk.II works well. No modification was required on the lens itself other than removing the bayonet plate and baffle piece, so the lens can be reassembled back to its original configuration without difficulty. Some of the machining was difficult, mainly with my unfamiliarity working with aluminium, using an unfamiliar lathe without any form of digital readout, and cutting the bayonet groove.
The aperture is controlled by the aperture ring, and although the distance scale on the focusing barrel is probably not accurate now, it's close enough. I do have trouble manually focusing with accuracy, and I've been using a monocular to try and dial it in, but it's still hit and miss at the moment ( during the commissioning stage of the project, anyway ).
Was it worth it? For a proof of concept, a fun challenge and an opportunity to use a lathe again - then yes, it was. In regards to perfomance, I'm not so sure.
I have done a quick test against the Mamiya 35mm, and although the test was nothing fancy or formal, there isn't that much between the two when stopped down; or at least the difference was less than I had expected. The Pentax is the better performer by a bit of a margin at lower apertures, but this margin closes up at higher apertures. Again, this is hardly an exact test, and there may be issues with where I have focused, etc., and I'll probably do some more testing both indoors and outdoors later on - this may make more of a difference in other scenarios.
Disclosure - I have no idea whether either of these lenses are "good copies" or not.
Anyways, with access to a machine shop and a free day, then Yes, the Pentax lenses can be adapted. Is a normal adapter possible without the need to disassemble the lens? I would have to sit down and really crunch some numbers; but without properly 3D modeling a concept, I doubt it. Is adapting the lens worth it? Hmmm, I'll let the individual decide on that one; but unless I can master consistent manual focusing, then maybe not.
Before I dived into medium format and began collecting a few lenses for my Mamiya ADF body, I looked into whether an adapter was available to convert the Pentax 645 glass to the Mamiya 645 mount, as my background is in Pentax and I'm reasonably familiar with the lenses. A lot of people had been asking the same question on forums for years, with the 35mm tending to be raised in conversation the most, due to reportedly being considered superior to the Mamiya in image quality and being a somewhat affordable wide-angle lens. Despite the interest, the answer was No, there is not an adapter.
So I looked into it a bit further and adapted a lens anyway. I purchased a good Pentax A 35mm, stripped the bayonet mount off it and machined up an adapting plate, including a bayonet. Overall, I'm happy that the thing actually works, as I completely bodged a Mk.I version of my adapter, but the Mk.II works well. No modification was required on the lens itself other than removing the bayonet plate and baffle piece, so the lens can be reassembled back to its original configuration without difficulty. Some of the machining was difficult, mainly with my unfamiliarity working with aluminium, using an unfamiliar lathe without any form of digital readout, and cutting the bayonet groove.
The aperture is controlled by the aperture ring, and although the distance scale on the focusing barrel is probably not accurate now, it's close enough. I do have trouble manually focusing with accuracy, and I've been using a monocular to try and dial it in, but it's still hit and miss at the moment ( during the commissioning stage of the project, anyway ).
Was it worth it? For a proof of concept, a fun challenge and an opportunity to use a lathe again - then yes, it was. In regards to perfomance, I'm not so sure.
I have done a quick test against the Mamiya 35mm, and although the test was nothing fancy or formal, there isn't that much between the two when stopped down; or at least the difference was less than I had expected. The Pentax is the better performer by a bit of a margin at lower apertures, but this margin closes up at higher apertures. Again, this is hardly an exact test, and there may be issues with where I have focused, etc., and I'll probably do some more testing both indoors and outdoors later on - this may make more of a difference in other scenarios.
Disclosure - I have no idea whether either of these lenses are "good copies" or not.
Anyways, with access to a machine shop and a free day, then Yes, the Pentax lenses can be adapted. Is a normal adapter possible without the need to disassemble the lens? I would have to sit down and really crunch some numbers; but without properly 3D modeling a concept, I doubt it. Is adapting the lens worth it? Hmmm, I'll let the individual decide on that one; but unless I can master consistent manual focusing, then maybe not.
