I've both of the bodies (F801 (non-s) & F601). With my 28-85 for example, the F601 seems more rapid and hesitates less. Maybe the F801 goes to far, then not far enough and repeats that cycle a few times for finally find the right distance. zzzzzzzzzzzzzzzzzzz(1)-zzzzz(2)-zz(3)-z(4) ----------------------> (1) <------ (2) ---> (3) <- (4) Jean-Pierre - Belgium