Turn off the preflash. I shot this in mid twilight. The f/stop allowed the background, already pretty dim, to go black. I manually focused on the plastic flower I chose and waited. Hummers are quick, and I would not depend on AF to keep up. Unlike race cars, the have a number of directions they can depart! BTW, this was shot with an old D200 and an aging 80-200mm f2.8 AF-D.