wide open vs other apertures, vignetting?

Hello,

I shot the first shot at 2.8, 1/4000 SS, and the 2nd at 9.0, 1/400 SS. both the same ISO. i took the shots so the exposure meter in the viewfinder was centered, taken w/ in a couple seconds of eachother. why does the shot @ 2.8 seem to have some vignetting or darker on the edges than the 9.0? is that normal? taken @ 24mm

2.8

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All fast lenses have noticeable vignetting when wide open, especially on full-frame cameras. (Lens designed for a FF camera but used on a crop camera will have less vignetting.) Use some software (like Canon's DPP, or Adobe Camera Raw) to automatically correct for this and other lens imperfections.

Light falloff on the edges. Pretty common wide open on full frame.