Sometimes when I switch to autofocus and I try to focus nothing happens. I put it to manual ans then back to auto and it will work. When it is on manual it dosn't always feel very smooth. If I point the lens down and try to manual focus I can hardly even turn it, it feels like it is on auto focus but it isn't. Anyone have any ideas? Is this a lens defect that B&H would just replace for me. The problem is I NEED this lens on nov 4 to shoot homecoming and I'm afraid since B&H is closed a lot right now due to holidays and their weird schedule I might not be able to get a new 1 in time.