Canon EOS Rebel T6i W Instruction Manual page 142

3 Correction of Lens Peripheral Illumination and Aberrations
When distortion correction is enabled, the camera records an image

range narrower than the one seen through the viewfinder. (Image
periphery will be slightly cropped and resolution slightly lowered.)
Distortion correction will be reflected in the captured image, but not in the

viewfinder or Live View image during shooting.
If you set [Distortion] to [Enable], the continuous shooting speed will

decrease.
Distortion correction cannot be set in the <F> or <G> mode, when

shooting a movie, or when Multi Shot Noise Reduction is set.
Dust Delete Data (p.272) will not be appended to images recorded with

distortion correction enabled.
Lens Correction Data
The camera already contains data for lens peripheral illumination
correction, chromatic aberration correction, and distortion correction for
approx. 30 lenses. If you select [Enable], the peripheral illumination
correction, chromatic aberration correction, and distortion correction will
be applied automatically for any lens whose correction data is
registered in the camera.
With EOS Utility (EOS 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.406).
For lenses incorporating the correction data, it is not necessary to
register the correction data to the camera.
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