I'm assuming that you are referring to MF 645 here. I have a 645AF with 150 and 210 ULD lenses. There are times when I would have enjoyed a better near-focus limit on both those lenses. I have resorted to using Nikon 5T and 6T diopters for close-focus work, and the sharpness on both lenses is still very good. But there is a gap in between "near without" and "far with" diopter. Also, diopters change the effective focal length, so that the lens is effectively a shorter focal length. That usually does not bother me, but sometimes it can be an issue. I have been looking for AF extension tubes locally, without success. So I would love to know whether someone else has tested diopters vs extension tubes for close-up work, from a perspective of both quality of results and ease of operation/use.