Canon 1D X - Manual (Page 68)

2: Selecting the AF Mode
68
This AF mode is suited for moving
subjects when the focusing distance
keeps changing. While you hold down
the shutter button halfway, the
subject will be focused continuously.
The exposure is set at the moment
the picture is taken.
AF is also possible by pressing the
<p> button.
Focus Tracking with AI Servo AF
If the subject approaches or moves away from the camera at a constant
rate, the camera tracks the subject and predicts the focusing distance
immediately before the picture is taken. This is for obtaining correct
focus at the moment of exposure.
When the AF area selection mode is set to 61-point automatic selection (p.69),
the camera first uses the manually-selected AF point to focus. During
autofocusing, if the subject moves away from the manually-selected AF point,
focus tracking continues as long as the subject is covered by the Area AF frame.
When you press the shutter button
halfway and the camera is focusing with
AF, the <i> icon will appear on the
lower right of the viewfinder.
In the One-Shot AF mode, the icon also
appears after focus is achieved when
you press the shutter button halfway.
AI Servo AF for Moving Subjects
AF Status Indicator
With AI Servo AF, the beeper will not sound even when focus is achieved.
Also, the focus confirmation light <o> in the viewfinder will not light up.
The AF status indicator can be displayed outside the viewfinder’s image
area (p.101).
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