Canon EOS 5D Mark IV L-series Zoom Lens Kit Owner's Manual

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f
 Automatic Sensor Cleaning
 
In step 2, select [Auto cleaningf] and set it to [Disable].
X
The sensor will no longer be cleaned when you set the power switch 
to <1> or <2>.
Disabling Automatic Sensor Cleaning
 
For best results, perform the sensor cleaning with the camera placed 
upright and stable on a table or other flat surface.
 
Even if you repeat the sensor cleaning, the result will not improve much. 
Immediately after the sensor cleaning is finished, the [Clean nowf] 
option remains disabled temporarily.
 
Dots of light may appear on images if the sensor is affected by cosmic 
rays, etc. By selecting [Clean nowf], their appearance may be 
suppressed (p.571).