I had my 30D on a tripod with a Tamron 2.8 28-75 lens and plastic diffuser on it. The tripod had only one segment of leg(s) extended so it was only about a foot or so off the hardwood floor. Anyway my crazy little nephew must have gotten to it when no one was around. I found the camera on the floor with the plastic diffuser broken. I don't think he pounded on it or anything...more likely just tipped it over. Since then, my shots don't seem to be quite as sharp -- though I'm not sure that's not just me being paranoid. I also noticed that I could wiggle the very end of the lens a little bit (maybe a quarter of a millimeter?) -- not sure if it was that way before the accident. Everything else seems to operate as before. Also, what is a logical range of cost for having Tamron calibrate or repair this lens?