Canon EOS-1D X Mark III Advanced User's Manual page 395

5.
Check the result of the adjustment.
Take a picture and view it (
Adjust toward "+:
position, and adjust toward "–:
Repeat the adjustment as necessary.
Caution
If [All by same amount] is selected, separate AF adjustment will not be possible
for the wide-angle and telephoto ends of zoom lenses.
) to check the results of adjustment.
" to correct focusing in front of your targeted
" to correct focusing behind it.
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