Canon EOS-1D X Mark III Af Setting Manualbook page 93

Shutter-release parameter for One-Shot AF
Set in the [AF3] tab
[One-Shot AF release priority]
[Focus priority]
You cannot shoot a picture unless it is in focus. It is effective
when you want to shoot only after focusing on the subject.
Release priority]
[
Priority is on the shooting timing rather than focus. It is
recommended only when you want to put priority on
capturing the image as quickly as possible.
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