Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 660)

6.
Focus on the subject.
When using autofocus
To start AF with [ AF button ] selected in the [ AF for still photo
shooting ] menu, select the (13) AF button.
If you selected [ Shutter button for AF/shooting ] on the [ AF for still
photo shooting ] menu, when you select the Shutter button (4) AF is
performed and a picture is taken.
When focusing manually
To show/hide (25) MF button display, select (5) MF toggle button.
Select (25) MF button, then focus manually. To adjust focus toward the
foreground, use [
], and to adjust focus toward the background,
use [ ].
Three levels of focus adjustment are available.
[
] [ ]: Coarse
[ ] [ ]: Intermediate
[ ] [ ]: Fine
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