I did some pics recently but i think they are gone when I clean house in flickr. Can't do any tests coz I sold the lens a while back.
Anyway, summary is, if subject distance is around 1 to 1.5 meter away, and aperture is F2.8, there is no detectable vignette. If wide open and subject distance is 1-3m vignette is minimal. If wide open and distance is 3 to 5, medium vignette (still correctable). If more than 5m and aperture is smaller than F4, heavy vignette.