I got a 70-200mm f4 (non IS) on the advice of OT and I've been playing around with it and I think there may be a problem with it, although I'm just not sure (newbie!). There seems to be some blurring at certain points in the lens. I've 3 photos all at different apertures and the blurring isn't as visible with a smaller aperture, but it is noticeable. The pics were taken on a tripod at 200mm, I'm using a 40D. These are just test shots, I'm not stalking the neighbours Shot 1: F4 Shot 2: F9 Shot 3: F18 If you look at the concrete wall on the right, the part beside the window is blurred a little, then it returns sharp as you move right and then gets blurry as you move to the drainpipe. There are a few areas where ghosting is at f4 (drainpipe, cut outs in the windowblind), but is this from being wide open? Any advice is appreciated.