Originally posted by Kguru Can someone please explain how 51 autofocus points work?
Does that mean it would preferentially shoot at f/16 for max dof to ensure all 51 points are in focus, or does it give us a choice to pick out of 51 points together with a super-quick method to indicate which one (like eyeball control)?
Thanks.
There are two ways the 51-point autofocus can be used.
a) Manually select, using the control buttons, which of the 51 points to use, the same way you can manually select which 11-point focus on the Pentax. Personally I don't think this method provides any real practical advantage with 51 points.
b) Set it to auto-select. The camera makes a "best-guess" focus out of 9, 21 or all 51 (user selectable). This works the same way as Pentax's Auto Focus Point select.
It does have practical use in fast changing action scenes where you just do not have time or predictability to focus-lock then and recompose. Even toddlers can provide a focusing challenge in such a situation.
You point the camera in the general direction to take the shot, then let the camera optimise the focus on the overall scene. It usually focuses on the nearest objects.
Having 21 or 51 points to optimise the focus does do a better job compared to 9.