I've been wanting to do some close-up/macro work with my Mamiya 645E, and a diopter only gives me some close-focusing. So, I recently acquired a set of extension tubes for my Mamyia from KEH.com, which remains #1 on my list of reputable sellers. I have never been disappointed with anything I have purchased from them. The last time I did macro in medium format was about 7 years ago with my Pentax 6x7. I wasn't terribly happy with my results then, but I'll attribute that to lack of experience. The 645 is a lot easier to handle, of course, and has better metering than the humongous Pentax 6x7. I also shot the images with TechPan -- the slowest emulsion available, but also the finest-grained. I have to say that I was really pleased with my results. All done on a tripod, of course, with mirror-lockup. The results:
"Spilling the Beans"