Canon EOS-1DX Instruction Manual page 75

61-point automatic selection AF
All the AF points are used to focus.
With 61-point automatic selection AF or Zone AF, the active AF point
<S> will keep switching to track the subject in AI Servo AF mode.
However, under certain shooting conditions (such as when the subject is
small), it may not be able to track the subject. Also, in low temperatures,
the tracking response is slower.
With Single-point Spot AF, focusing with the Speedlite's AF-assist beam
may be difficult.
If you are using a peripheral AF point or a wide-angle lens, achieving
focus with the EOS-dedicated Speedlite's AF-assist beam may be
difficult. In such a case, select an AF point close to the center.
When the AF point(s) lights up, part or all of the viewfinder may light up in
red. This is a characteristic of AF point display (using liquid crystal).
In low temperatures, the AF point's blinking (p.72) may be difficult to see.
This is a characteristic of AF point display (using liquid crystal).
With [24: Orientation linked AF point], you can set the AF area
selection mode + AF point (or only the AF point) separately for the
horizontal and vertical orientations (p.101).
With [24: Selectable AF point], you can change the number of
manually selectable AF points (p.99).
With One-Shot AF, pressing the shutter button
halfway will display the AF point(s) <S> that
achieved focus. If multiple AF points are displayed,
it means they all have achieved focus. This mode
tends to focus the nearest subject.
With AI Servo AF, the manually-selected (p.71) AF
point <S> is used first to achieve focus. The AF
point(s) achieving focus is displayed as <S>.
AF Area Selection Modes
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