Canon EOS-1D X Mark III Advanced User's Manual page 800

2.
Select [Clean now ].
Select [OK] on the confirmation screen.
Note
Even if you repeat the sensor cleaning, the result will not improve much. Note that
[Clean now ] may not be available immediately after cleaning.
Dots of light may appear in captured images or on the shooting screen if the sensor
is affected by cosmic rays or similar factors. By selecting [Clean now ], their
appearance may be suppressed ( ).
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