Canon EOS-1D X Mark III Advanced User's Manual page 409

Caution
Under difficult shooting conditions for AF (
displayed correctly.
No AF points are displayed while the guide frame is displayed.
No adjustment information is detected for apertures darker than f/8 when MP-E
65mm f/2.8 1-5× Macro Photo is used or darker than f/11 for other lenses, as
indicated by the Focus Guide appearance.
The guide frame is not displayed in these situations.
• When the lens's focus mode switch is set to <
• When display is magnified
The guide frame is not displayed correctly during shifting or tilting of TS-E lenses.
Note
The camera's auto power off counter does not count time spent adjusting the focus
with a lens's electronic focusing ring.
Adjustment information not detected
), the guide frame may not be
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