I ran into a rather strange problems when using my D300 with the Nikon 70-300VR lens. If I use a circular polarizer on the lens I can only get out of focus images. If I take the polarizer off it focuses fine. I have tried manual focus, Liveview Tripod mode and normal AF with the same result. I had the camera mounted on a tripod with VR off and used shutter delay, just to be safe. I was shooting outside during a very bright day. F5.3 at 200mm and around 1/120 I believe. I don't mean a little soft, I mean very out of focus. I suspect it is the filter. It's not a real expensive one (Sunpak) but I would have never guessed it would be that bad. It appears clear and undistorted to look thru it. I even cleaned it, which made no difference.