85L and "chopped bokeh"

Ok, perhaps it's not vignetting, but,

"Bokeh characteristics may be quantified by examining the image's circle of confusion. In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc."

and as this "round disk" receives light coming coming in from the sides, the blur disk takes on the shape of the aperture at that angle, which is the effect you get with the 85L.

In fact, this doesn't even need discussion, anyone who has a good understanding of airy/blur disks should know why it happens right away.

Oh come on now LOL, great bokeh has soul, the 85L bokeh has soul and I think it's a combination of more than just the dof, which includes the way it handles color and contrast and because it just is such a great piece of glass. My 135L also has bokeh soul. Yes it's a math thing technically but the final outcome esthetically depends upon what the person likes.

I would really like to have the opportunity to try a 50mm Sigma on my MKIII. I like the bokeh that I've seen from that lens so far