Make sure you are familiar with the AF functions of the camera. Birds in flight while shooting in ONE SHOT will yield soft images. Also try to keep shutter speeds above 1250. There is a lot to learn about DSLR AF systems so understanding that is important. The original 100-400 is a fantastic lens, I shot mine exclusively off a tripod and would put those images up against many I saw from "sharper" lenses. It did take me some time to learn to shoot it properly though. Good luck
