Does VR work with extension tubes then, Pierre?
Yes it does. I put the 3 extensions + the TC-20E3 on the 105mm and autofocus/VR works just fine, the assembly becomes 10 inch long. You can really get close to your subject and have good magnification. Sure lot better shots could be done with a pinned-down butterfly and proper lighting but I am against violence :^) I haven't got a chance to try my focusing rail yet.