i picked it up for $400. The reason i went for it over the canon 28mm was watching a video on vimeo that i loved.
i emailed the guy with the lens, and he said he owns 50 lens, and this 28mm f2 was his favorite.
after watching it, and comparing it to the canon, i was sold. And i didn't know i would have to cut the aperture until after i purchased it. I searched randomly on ebay, and there was this exact lens with 30min left, and i won the bid. Again, i plead ignorance.
as for the sigma or vivtar lens, i nothing about them. I'm the kinda of guy who buys random things on ebay, and this time around i probably shouldn't have been the winner of this lens. I really didn't know better.