the way i understand it ae = auto exposure, af = auto focus. so depending how you set the ae/af button when you press it it locks which ever you have it set ( one or the other or both) and then while holding the button down you can recompose a shot and keep the focus and exposure the same.


not supre useful if your using single servo focus or manual exposure... but can still be very usefor for getting quick pics while in auto modes.