Canon EOS Rebel T4i 18-135mm IS STM Lens Kit Instruction Manual page 129

3 Lens Peripheral Illumination / Chromatic Aberration Correction
About the Lens Correction Data
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 is 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
Software Instruction Manual (CD-ROM) for EOS Utility (p.352).
Notes for Peripheral Illumination Correction and Chromatic Aberration
Correction
Corrections cannot be applied afterwards 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 shown on the screen.
If the effect of the correction is not 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
[Disable].
If the lens does not have distance information, the correction amount will
be lower.
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