Solution
What is lens peripheral illumination correction?
Due to the lens characteristics or shooting conditions, the four corners of the picture might look darker. This is called lens light fall-off or drop in peripheral illumination.
To correct images that are affected by lens peripheral illumination, you can either set the correction setting on the camera before shooting, or you can import the images to a computer and edit them after shooting.
The default setting is [Enable].
JPEG images are corrected during shooting if you make the following setting beforehand.
For RAW images, it can be corrected with Digital Photo Professional.
For details, refer to the Instruction Manuals. Instruction manuals and software can be downloaded from the Canon Web site.