I know that photograppy is about the user and not the camera but when I have been taking pictures of birds in flight my camera can't hold a focus point. I have it set up for back button focusing in Aperture Priority set to AF-C. I have tried the Dynamic, 3D and Auto focus modes to no avail. The focus light indicates a focus lock so I fire the shutter but when I look back in Capture NXD there is no focus point. Should I stop using back button focusing? My reason for saying this is that when I hold down the back button it will try to adjust the focus constantly. Is this why the shots aren't so good?