I have been experimenting with extreme macro a bit recently. I've tried Fotodiox bellows, which is a real pain with Nikon lenses that don't have aperture rings and default to the smallest possible aperture. You have to reverse mount them and jam something into the back of the lens to force the aperture tab open. The Fotodiox bellows are quite flimsy, so they bounce around when you adjust the focusing rail. I probably should have gotten a used PB-6, which is more rigid and allows you to operate the aperture tab using one of the old-fashioned mechanical cable releases (which I still have from my Crown Graphic days.) I have had the best luck so far with lens stacking. I use a Nikon 70-200 f/4 on my D500 and reverse-mount a Sigma 18-35 f/1.8 to it. At 18 and 200, the magnification is about 11:1. Here's a sample of the results. It's a ~2 mm section of a butterfly wing.
