I figure some may know this already, but this is just good knowledge to keep on spreading. Basically ef-s lenses only differ from ef lenses due to some additional rubber on the rear end of the ef-s lens. To convert it all you need to do is pull the rubber piece out. Here is what I found on the subject: http://www.flickr.com/groups/canondslr/discuss/72157604422834954 Now you can use great ef-s lenses like the 10-22mm on your full frame lenses. With the 10-22mm, however, you don't want to zoom out past 12mm. Seems the 17-55mm ef-s works without a hitch.