I have been spending more time reading and playing with the custom settings on the MKIII and am confused on the custom functions C.Fn III-4 and C.Fn III-5. When reading the manual and the optimizing 1D series pdf they seem to do some what the same thing. i have been playing around with III-4 and I can not see any difference what so ever in the way the AF acts.
Is anyone using these settings and if so do you and when do you see a difference.
My english knowledges are not good, but I try to answer as I understand these two. In C.Fn III-4 you can choose between 0 and 1. With 0 the active AF-point changes to main AF-point and with 1 it will not notice objects in front.
In C.Fn III-5 you can choose if the AF is on with 0. This is important if it doesn't find the AF point it will continue to search and you cannot take any photo. With 1 you can take this search off.
For me it is a difference. With the first one you choose how it will autofocus and with the other you can choose what it will do when it cannot find any autofocus point.
0 - will try to refocus if any object comes between you and the original target
1 - will try to maintain focus on the original target even if something comes between it and the camera
Best example is that you are following a wide receiver and an annoying safety comes in between you and the receiver. With #0 the focus will shift to the safety and with #1 the focus will stay on the receiver.
C.Fn III-5
0 - will continuously try to find a focus point
1 - will stop trying to focus if it loses focus
Say you are tracking a flying bird and lose contact. #0 will try to focus on whatever is under the selected AF point, in this case the sky which will send the focus all over the place searching for something to home in on. #1 will stop trying to focus which can make it much faster to re-focus once you reacquire the target because the focus hasn't spun too far from where it needs to be.
