Canon EOS-1D X Mark III Af Setting Manualbook page 74

How to distinguish between cross-type
AF points and horizontal/vertical-line
focusing AF points.
To distinguish between cross-type AF points and horizontal/
vertical line focusing AF points, attach the lens to be used
and select the AF point. If the AF point does not blink,
cross-type AF is performed, and if it blinks, then horizontal-
line or vertical-line focusing AF is performed. If you want
to use cross-type AF with higher capture performance,
confirm the cross-type AF and select the AF point.
AF points that are not cross-type AF points will blink so
that they can be distinguished when attaching a lens.
Cross-type AF points
Does not blink
Horizontal-line or
vertical-line focusing
AF points
Blinks
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