Canon EOS 6D Instruction Manual page 310

3 Custom Function SettingsN
C.Fn II -6
If focus cannot be achieved with autofocus, you can have the camera keep
searching for the correct focus or have it stop searching.
0: Continue focus search
1: Stop focus search
If autofocus starts and the focus is far off or if focus cannot be achieved, the
lens drive stops. This prevents the lens from becoming grossly out of focus
due to focus searching.
Super telephoto lenses can become grossly out of focus during continuous
focus search, taking more time to achieve focus the next time. Therefore,
setting [Stop focus search] is recommended for super telephoto lenses.
C.Fn II -7
Instead of using the same AF point for both vertical and horizontal shooting, you
can select and use different AF points for both.
0: Same for both vertical/horizontal
The AF point you select manually will be used for both vertical and horizontal
shooting.
1: Select diffent AF points
The AF point can be selected separately for each camera orientation (1.
Horizontal, 2. Vertical with the camera grip at the top, 3. Vertical with the
camera grip at the bottom). Convenient when, for instance, you want to keep
using the right AF point during all camera orientations.
When you manually select an AF point in one of the three orientations (1., 2.,
or 3.), this setting will take effect. When you change the camera orientation,
the AF point will also change to the AF point corresponding to the one you
selected manually.
C.Fn II -8
0: On
1: Off
When focus is achieved, the AF point(s) in the viewfinder do not light up in
red. Set this if the AF point's red light-up is bothersome.
The AF point will still light up in red when you select it.
310
Lens drive when AF impossible
Orientation linked AF point
Superimposed display