OK, this is probably me doing something stupid but when I tried to use my recently acquired E28 extension tube today on both my ETR and ETRSi bodies, I couldn't get the lens to focus. I don't have a manual but the seller jotted down some instructions on connecting it to the lens and body, which I followed and appeared to do correctly since all connected up OK. However when I turned the lens to focus nothing changed and everything was out of focus. Now I did try it with my 50mm lens since it was the only one to hand, would it be this (I need to dig out my 75mm lens to test) or is something else not quite right? Any suggestions appreciated.