Every now and then I will take several shots using my D200 and 17-55mm f/2.8 which all turn out to be 'out of focus'. There just doesn't seem to be anywhere in the image that is in focus. I originally thought there was a problem with the lens/camera. However, I have had plenty of ultra-sharp images from this lens. The only explanation I can come up with would be blur from camera/lens shake due to the lens being very heavy. I don't seem to have this problem with any of my other lenses. Does anyone else have experience of this problem with this lens?