I just got a 2nd hand 70-200 F4 IS and it is quite soft at 200mm until around f8. I owned a non IS version in the past it it was very sharp at f4- so I feel there is something absolutely wrong with it (no part is sharp so I know it's not a MA issue, I've tried both of my bodies with the same result, shot from a tripod during a sunny day is on and off, SS above 1/1000). So.... I'm curious what the options are, I've never had to send a lens off, what am I looking at as far as potential solutions as well as costs involved in sending it in? Any help would be great!