Out of curiosity, and after reading several times about the higher optical quality of the Ai/AiS version (which, supposedly identical, at least in design, to the AFD), I have had the opportunity of performing a fast dirt test, wide open and f8. I`m in a hurry, so no time to make it better. I was convinced my AFD was at least more contrasty; the only difference I have found is that the Ai at f8 transmit a bit more light than the AFD. I must say that the Ai is way more used, both lenses bought new time ago. The AFD is in very good shape. I took several pics to compare focus, all pics taken with Live View. The AFD version is really difficult to focus manually, as it shows the classic AF "shift" or "jump". The Ai, a pleasure in comparison. Wide open, I cannot see any difference. At f8 the Ai looks very slightly sharper, but I suspect it could be the mentioned focus problem, or maybe a decentering issue. Anyway, I think that difference is negligible.