As I am sure you realise by now one needs to be very close to a small bird to get a usable image. To be able to get into a position to even attempt a shot a hide (blind) or camouflage and patience is necessary. Another prerequisite is to know your quarry, it's habitat, behaviour etc. As regards small birds in bushes manual focus is your answer. You have control. When you adjust focus and the bird's head and eyes leap into a crystal clear shot it's a great feeling. Use cable release and a tripod. It isn't easy but the rewards are great. Hope this helps. Good hunting as that's what it is!