I recently returned a new 24-105L to Canon because of soft images. Quality was distinctly inferior to 3 other lenses I own (Canon 28-135 IS, Canon 70-300 IS, and Sigma 17-70). All of these are decent lenses, but I don't think anyone would expect them to compare favorably with the 24-105L (with the possible exception of the 70-300 sometimes). Canon returned it, said they checked and cleaned it (it was brand new, wasn't "dirty") and if the problem recurred to return it with the camera body. But the camera body works fine with the other lenses. Is there any reason to think there is some issue with the body (Rebel XSi/450D) that would cause problems with this lens and not another? Or is this just Canon not wanting to replace an obvious lemon of a lens? Any insights appreciated.