Here is the 20D with the 580 EX flash and the 100-400mm f5.6 IS L lens. Note the push-pull zoom design. When I went to my local camera store looking for a telephoto primarily for birding, I assumed I would get a prime lens (the 300mm f4 or the 400mm f5.6 that Daniella likes) due to reviews like this that show primes to be sharper than the 100-400 zoom. But I found that 300mm was way too short, and I couldn't hand-hold without IS, so I surprised myself and ended up with the 100-400. Soon after, I found that premier bird photographer Art Morris had reneged on his recommendation of the 400 f5.6 prime, and now favors the 100-400. Since then Artie has gone back and forth on his favorite "toy" lens, favoring the 400, the 100-400, or the 70-200 f2.8 at different times.