Have you ever used an APS-C lens on a full-frame camera? This is the vignetting that happens when you do.

Canon EOS 5D Mk 4, Tokina AT-X 116 PRO DX ll 11-16mm F2.8

f11, 1/250 sec, 11mm, ISO 200, Processed in Silver Efex.

More of my photography can be found on my website and my blog.