Canon EOS 6D Instruction Manual page 316

8: AF Microadjustment
2: Adjust by Lens
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 has been registered,
the point of focus will always be shifted by the adjustment amount.
Set the adjustment manually by adjusting, shooting, and checking the
result. Repeat this until the desired adjustment is made. If you use a zoom
lens, make the adjustment for the wide-angle (W) and telephoto (T) ends.
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1 Select [2: Adjust by lens].
Select [2: Adjust by lens].
2
Press the <Q> button.
The [2: Adjust by lens] screen will
appear.
3
Check and change the lens information.
Check the lens information.
Press the <B> button.
The screen will show the lens name
and a 10-digit serial number. When
the serial number is displayed, select
[OK] and go to step 4.
If the lens' serial number cannot be
confirmed, "0000000000" will be
displayed. Enter the number as
indicated below. See the next page
about the asterisk " * " displayed in
front of the lens serial number.