You want the older M645 manual focus, MANUAL aperture, non-D model.
The current D version, while optically identical to the older unit and still MANUAL FOCUS, has an electronically controlled aperture (like a Nikon G lens or a Contax 645 lens) and can't be used on an SLR. If on eBay, etc., trust and verify as many folks get sloppy in the naming of the lens or get liberal in the naming to help with keyword searches as the older lens can be used on a newer camera, etc:
- Remember ALL versions of this lens, even the one they sell new today for the DF cameras and backs, are manual focus, so that's no differentiator.
- Make sure the image of the lens shows a physical aperture ring and is labeled M645 with no "D"
- Price also helps narrow initial searches - the older versions will cost less than the new D .
GREAT lens (I'd say the same about all my M645 glass). Just something about how they draw vs other, typically far more costly, alternate glass I've owned. Also have to remember that while the prices today are low (at least until lately) for how well they deliver, it's solely because the M645 line was discontinued. Some of these lens were well into the multiple thousand $$ when new - back when $3000 meant more than it does now ;>