Sometimes I want to use manual focus on my native, autofocus lenses (14, 20, 14-42, 40-150) but I don't because, as I understand it, when I move the ring, it operates a wire (?) which then moves the motor which in turn moves the glass? The exception is the Sigma 30. When I put that on manual it's very good and easy to focus and isn't jumpy like the rest of them. Why is this one different? Also, the 12mm f2 has a little ring to click it into MF mode. Is that REAL MF or focus by wire? I heard it's ALMOST like MF but not really and is not fly by wire. I'm confused. It looks like the 12-40 is going to have the same thing. Thanks!