No the actual rear element hits at 18mm not the EF-S plastic, I cut that off long ago, if you do a google search there's a bunch of 10D owners who also had theirs hit at 18mm. I'm guessing the quality control of the taiwan lenses were not all the same and some are a hair longer.
It hit the mirror at least 6 times before I noticed, nothing broke and the lens didn't even get a scratch or wear off the coating. Theses mirrors are stronger than you think, in the MF thread there's guys who have hit their 5D/5DM2 mirrors on M42 lenses before and nothing broke. These lenses and mirrors are tough.
Of course after I found out that it hits I don't shoot at 18mm anymore, I would like to put a limiter in the lens so that it stops at 19mm, here's the video I was talking about. If you watch it you'll notice the stop is now at 19mm instead of 18mm.
http://www.youtube.com …_piwP9MxGc&feature=g-hist
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