Ok, I had the Tamron 70-300 VC and you should be able to shoot it just about wide open. A few thoughts. Are you waiting a sec for the VC to engage? The last eagle shot has a strange look to it. Try this, in the AF menu A1, set AF-C to Focus Priority (you will get less shots but the camera won't fire until the subject is in focus). On menu B1 ISO Auto, Set minimum shutter to 1/1250th Max ISO to 400 and turn it on. (if your camera doesn't show anything higher than 1/250th you don't have the latest firmware update) Shoot in "A" mode and the camera will try to keep your shutter above 1/1250th. Try shooting in AF Dynamic (third group down on the rear selector) make sure menu item a3 is set to normal and a4 is set to center area. Another thing to try is using back-button focus (AF-ON) this allows you to control the AF system with your thumb and gives you more control.... Have fun