Here’s one with the same lens (Canon 50 f/1.4), on the same 5D, that I shot last weekend, with similar lighting…bright and contrast on subjects, but what I see in it is on the right hand side, the OoF tree... it was close, like the cat was close, it seems to have the same type of halo effect…
Shot at f/2…in both photos…the tree was about the same distance as the cat from the lens in both shots…the angle would be about the same…I was using the tree to block the sun when I shot the second photo…the cat was blocking the sun in much the same way.
Not a crop.
Maybe that’s a characteristic of the 50 f/1.4 when shot at shallow DoF with those parameters...maybe any fast lens...