Canon EOS 5DS Instruction Manual page 190

3 Correction of Lens Peripheral Illumination and Aberration
Cautions for Lens Correction
Peripheral illumination correction and chromatic aberration correction
cannot be applied to JPEG images already taken.
When using a non-Canon lens, setting the corrections to [Disable] is
recommended, even if [Correction data available] is displayed.
If you use magnified view during Live View shooting, the peripheral
illumination correction and chromatic aberration correction will not be
reflected in the image shown on the screen.
The correction amount will be less if the lens used does not have
distance information.
Notes for Lens Correction
If the effect of the correction is not visible, magnify the image after
shooting and check it again.
Corrections can be applied even when an Extender or Life-size
Converter is attached.
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