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Jerry, perhaps someone else can chime in with that C function because I've never used it.
I think zone AF can work well if the background doesn't compete against your target for AF's "attention".
That means the background is either "smooth", or it is very distant.
Also, for close target zone AF, gotta have plenty of DoF because you have no control on the parts of the target that the camera will focus on. In theory it should AF on the closest contrast, but in practice it is pretty scattered.
Also, see those two illustrations below. They are full frames taken...Show more →
Peter, have read a bit more on the C "Mode Dial" set functions (the 1D pro bodies don't have a mode dial) and AF functions/settings along with most all settings are saved for future use; like they are on my 40/50D. Your 7D can do this, I'll take a closer look at it's and the 5D3's AF systems.
Thanks for the visuals, BIF images, they helped, explained why I get more keepers shooting airplanes, birds, kites or anything in the sky, then when shooting surfers. All that pounding water, foam n spray can be quite distracting, not to mention those bikini clad birds that seem to...zone AF might help...maybe