Canon MARK IV User Manual (en)

Lens Peripheral Illumination Correction
The camera already contains lens peripheral illumination correction 
data for approx. 25 lenses. In step 2, if you select [Enable], the 
peripheral light correction will be applied automatically for any lens 
whose correction data has been registered in the camera.
With EOS Utility (provided software), you can check which lenses have 
their correction data registered in the camera. You can also register the 
correction data for unregistered lenses. For details, see the Software 
Instruction Manual (CD-ROM) for EOS Utility.
About the Lens Correction Data
For JPEG images already captured, lens peripheral light correction 
cannot be applied.
Depending on shooting conditions, noise might appear on the image 
When using a third-party lens, setting the correction to [Disable] is 
recommended, even if [Correction data available] is displayed.
Lens peripheral light correction is applied even when an Extender is 
If the correction data for the attached lens has not been registered to the 
camera, the result will be the same as when the correction is set to 
The correction amount applied will be slightly lower than the maximum 
correction amount settable with Digital Photo Professional (provided 
If the lens does not have distance information, the correction amount will 
be lower.
The higher the ISO speed, the lower the correction amount will be.