Canon EOS-1D X Mark III Advanced User's Manual page 396

Adjusting for Individual Lenses
You can make the adjustment for each lens and register the adjustment in the camera. You
can register the adjustment for up to 40 lenses. When you autofocus with a lens whose
adjustment is registered, the point of focus will always be shifted by the adjustment amount.
Keep adjusting, shooting, and checking the results to set the adjustment amount manually. If
you use a zoom lens, make the adjustment for the wide-angle (W) and telephoto (T) ends.
1.
Select [Adjust by lens].
2.
Press the < > button.
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