Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 399)

4.
Make the adjustment.
Single focal length lens
Zoom lens
For a zoom lens, select the wide-angle (W) or telephoto (T) end.
Pressing <
> clears the purple frame and enables adjustment.
Set the adjustment amount, then press < >. The adjustment range is
±20 steps.
Setting it toward “–: ” will shift the point of focus in front of the
standard point of focus.
Setting it toward “+: ” will shift the point of focus to behind the
standard point of focus.
For a zoom lens, repeat this procedure and adjust it for the wide-angle
(W) and telephoto (T) ends.
After completing the adjustment, press the < > button to return
to the screen in step 1.
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