Canon EOS 5D Mark III Instruction Manual (en)

 Lens Peripheral Illumination / Chromatic Aberration Correction
The camera already contains lens peripheral illumination correction 
data and chromatic aberration correction data for approx. 25 lenses. If 
you select [Enable], the peripheral illumination correction and 
chromatic aberration 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, refer to the EOS 
Utility Instruction Manual (p.396).
Notes for peripheral illumination correction and chromatic aberration 
About the Lens Correction Data
Corrections cannot be applied to JPEG images captured when [Disable
was set.
When using a non-Canon lens, setting the corrections to [Disable] is 
recommended, even if [Correction data available] is displayed.
If you use the magnified view during Live View shooting, the peripheral 
illumination correction and chromatic aberration correction will not be 
reflected in the image.
If the effect of the correction is not so visible magnify the image and 
check it.
The corrections are also applied when an Extender is attached.
If the correction data for the attached lens is not registered to the 
camera, the result will be the same as when the correction is set to 
If the lens does not have distance information, the correction amount will 
be lower.