Hi All, just playing with my new (old) 1dsMKII - I am most concerned with my ability to lock on a dancing person in low light with a speedlight on top of the cam. Do you ever use this and when? Sounds good in theory.

C.Fn 17-1 expands the active focusing area by a radius of 1 point around the manually
selected focusing point, creating up to 7 active focusing points. The camera always
tries to use the manually selected focusing point, but when it can’t, it can choose one
of the other 6 active focusing points if there is readable subject detail under one of
them. This option is intended to increase the odds of getting sharp photos with small,
fast moving subjects such as birds in flight. However, it can sometimes cause critical
focus to shift slightly ahead of or behind relatively large 3-dimensional subjects like
human beings.

I have it in my "My" menu on my 1D3. I turn it on and off depending on circumstances. It helps with motion tracking for those kind of shots, but I find it jumps me off-focus too much for still shots and often turn it off.

I have it turned on, on my 1DmkIII all the time. I find it to be great.