Canon EOS REBEL T7i Instruction Manual page 178

3 Correction of Lens Aberrations due to Optical CharacteristicsN
Cautions for Lens Correction
Peripheral illumination correction, chromatic aberration correction,

distortion correction, and diffraction 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.
The correction amount will be less (except for diffraction correction) if the

lens used does not have distance information.
Notes for Lens Correction
The effect of the lens aberration correction varies depending on the lens

used and shooting conditions. Also, the effect may be difficult to discern
depending on the lens used, shooting conditions, etc.
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.
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] (except for diffraction correction).
In Basic Zone modes, peripheral illumination correction, chromatic

aberration correction, and diffraction correction will be applied
automatically. Distortion correction will be applied automatically only in
the <q> mode.
178