Canon EOS-1DX Instruction Manual page 221

You cannot take a picture during autofocusing. Take the picture while the
Live View image is displayed.
3
Select the AF point.
Use the <9> to select an AF point. If
you press <9> straight down, the
center AF point (or center Zone) will
be selected.
You can also use the <6> and
<5> dials to select the AF point. The
<6> dial selects an AF point in the
horizontal direction, and the <5>
dial selects an AF point in the vertical
direction.
4
Focus the subject.
Aim the AF point over the subject and
press the shutter button halfway.
The Live View image will turn off, the
reflex mirror will go back down, and AF
will be executed. (No picture is taken.)
When focus is achieved, the beeper
will sound and the Live View image
will reappear.
The AF point used to focus will light
up in green.
If focus is not achieved, the AF point
will blink in orange.
5
Take the picture.
Check the focus and exposure, then
press the shutter button completely to
take the picture (p.207).
Using AF to Focus
221