Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 320)

One-Shot AF for Still Subjects
This AF operation is suited for still subjects. When you press the shutter button halfway, the
camera will focus only once.
Viewfinder shooting
• Once a subject is in focus, the focusing AF point (1) flashes in red, the focus
indicator (2) < > in the viewfinder lights up, and the camera beeps. The focus
indicator < > blinks if the camera cannot focus.
Live View shooting
• Once a subject is in focus, the focusing AF point turns green and the camera beeps.
If focus is not achieved, the AF point will turn orange.
Note
If [ : Beep ] is set to [ Disable ], the beeper will not sound when focus is achieved.
The focus remains locked while you hold down the shutter button halfway, allowing
you to recompose the image before taking the picture. This is called “focus lock.”
See
Lens electronic MF when using a lens that supports electronic manual
focusing.
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