My first shot ever taken with the 85mm f/1.2 II and attached EF 25 II Extension Tube. The idea of a f/1.2 macro-like lens was too tempting. And then I remembered why I had sold my old 100mm f/2.8 dedicated macro lens: you really need nerves of titanium and/or a monopod/tripod to do this stuff right. At this range and f-stop, any movement in any direction will ruin the shot.
Also tried to stick the extension tube onto my 35L. Practically unusable (unless I'm missing something) since it makes the minimum focus distance like less than an inch as far as I can tell.