Canon 50L bokeh bubbles out of shape? video inside!

Hello

When i shoot with my Canon 50L on my 5d II i've noticed a change in shape in the bokeh bubble as soon as the "bubble" goes off center.
The strange thing is that i don't have this "problem" with my Canon 50mm F1.8 ?
It's getting worse when i open up the aperture.

Made a small clip with my 5d, watch the edge of the "bokeh bubble" when it gets to the edge of the frame!
http://www.vimeo.com/1​0644392
I was just wondering if this is "normal" with the 50L on FF ?
What causes this effect?

Who can test this on his own cam?
I've used some christmas lights about 2 feet away from the cam.

I don't know the technical terms but I think that would be expected as you look at the light rays coming in further from the center of the lens. You don't see a problem with the f/1.8? The circles all turn into footballs with the f/1.8 and in my opinion looks worse than the L.

Totally normal. You can see them with the 50mm f/1.8 as well. This happens to some extent with all lenses. OOF shapes that appear as circular in the center become more distorted at the edges.

Normal. This happens with the 85L as well.

@tim i ment that the bubbles are getting chopped off @ 50L and you don't see that with the 50 1.8
Thanks for the responses all

Should this effect get even worse or less due to the focal length?

Focal length should not make much of a difference. I think it has more to do with the design of the lens and the internal elements. IIRC, any lens wide-open will show more of this than when stopped down.

In the link below the explanation is that quote: "the mirror chamber of the SLR that Mike used is too small to support the speed of the lens".

http://toothwalker.org​/optics/bokeh.html