On my 40D my telephoto zoom has been the Canon 70-300, the but now has quite a dust problem and the manual focusing insert is much too easy. A reasonable substitute, I could imagine the long term only a Canon L lens to me. I have long wrestled with me, if a touch zoom is also really practical, because I was so far only usual rotation zoom. The weight was as rather irrelevant. Since I like to take pictures at air shows, the zoom range could ultimately not be large enough. Finally, the end of March I could bring myself to buy the 100-400 and the first major use came during the DTM opening weekend in Hockenheim. After a very short period of familiarization, I could imagine only one touch zoom for this zoom range. Functionality, image quality, and focusing speed anti-shake are first class! All recordings I made without a tripod, which would in many cases anyway disturbed. For the additional battery grip for handling the heavy objective was a significant gain. The freshly charged battery pack in the Stabilizer Mode 2 also has loosely held by more than 2,500 shots. I had to focus almost exclusively used to manually during fast action shots with the 70-300, so I have this time to photograph always in auto mode. Class! If you have seen the press photographers at the DTM attention to the lenses, you could see the 100-400 at practically every other photographer. And they know why. Strong buy recommendation for anyone who needs a big push and where 1.4 kg at bayonet not mind!
Addendum: Meanwhile, the lens also has its first air show insert behind. Particularly if several aircraft are photographed at once, I have to make mainly focus manually with the 40D. At the same time to use the zoom, initially requires some practice, but is easy to learn. The larger zoom you can finally take pictures full frame. The lens is just great!