Out on the job and my backpack zipper gave out and let my 70-200 and my 580ex flash slam into the concrete. Dropped about five feet where I was having to jog to get a picture so it took even more of a hit. When the two items contacted the ground the impacts made an awful sound that will haunt my dreams. Sounded like a light bulb being thrown onto the ground where they pop when the explode. Filters all bent up where it looks to have taken most of the damage but the internals are screwed and it will need to be sent into Canon. Anybody know of a circumstance like this where a lens looses some of its image quality or does Canon test it to see if it still achieves top notch image quality. I am so mad I could piss blood! At least my 5D2 and the 16-35 II lens where on the tripod at the time and not in my now ripped to pieces backpack.