Thanks for the info, Slingers! Regarding the 21, my experience is this. While it feels like it won't fit without trimming the feet, it will, but by the barest of margins. The trick is in which order you assemble the three parts. From memory you must put the lens on the adapter first, then the combo on the camera. That applied to my passive adapter, a Kipon. Bu adapter sizes should all be the same, in theory, and your electronic one should be high grade, so dimensionally correct. The issue then is corner performance, even with a 5N. While it is a tremendous lens, maybe the finest Zeiss glass ever to pass through my hands, I could never get a CornerFix profile to eliminate colour shift, never mind corner mush, so I sold it. But the guy who bought it produces stellar images with it...:-(