Thanks to both responders. I guess I read the information about Back Focus Adjustment as you guys did. So I am inclined to think the issue is really an issue with this lens. It seems to sharpen up at 300mm when I stop down to f8.0, But even then it's really not as crisp as I would like. In truth I think this is a design issue for most long zoom lenses. They all seem sharpest at the shortest focal length. My other system is a Panasonic G9 with the 100-400mm lens and it too is sharpest at the shorter FL. However, even at 400, it seem sharper than this Sony lens at 300mm.