In this video i show you a review of the canon 100-400mm l series lens with IS. and USM.
its fast focusing and is a massive telephoto lens and when worked along with the canon 550d and have it on the crop movie function where it uses the central 640/480 pixels then you have it at a 7 times zoom. and 7 times 400mm on a cropped sensor makes it about a 1000000000mm lens a bit like a telescope! you can make the zoom smooth or tight so that you dont have barrel creep when not using it.
not so great for portraits but shooting a snowboarder falling down a mountain across the valley it would be A MA ZUN!