Canon EOS-1D C Instruction Manual page 97

Lens drive when AF impossible
If focus cannot be achieved with autofocus, you can have the camera
keep searching for the correct focus or have it stop 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.
Selectable AF point
You can change the number of manually selectable AF points. With
automatic AF point selection, all 61 AF points will remain active
regardless of this setting.
3 Customizing AF Functions
ON: Continue focus search
If focus cannot be achieved with
autofocus, the lens is driven to search for
the correct focus.
OFF: 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.
: 61 points
All 61 AF points will be manually
selectable.
: Only cross-type AF points
Only cross-type AF points will be
manually selectable. The number of
selectable cross-type AF points will differ
depending on the lens.
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