400mm f/5.6L, the oldest lens still in the current lineup. Lightweight, well-balanced, fast AF, sharp, affordable - the perfect birding lens for beginners and those on a budget. ^ Yupp, I agree exactly with what she said!
How on earth can a telephoto lens without IS be described as a "perfect birding lens for beginners"? I would have missed 70-80% of my best photos of birds without IS. The lens' former greatest proponent Arthur Morris has long discarded it because lenses because it doesn't have IS.
I am not saying the lens is no good - it is excellent for birds in flight, and it is fine on a tripod. But, there are just so many opportunities, especially with small birds, where you have to be able to take shots at a 1/100 to 1/400s hand holding. The lens without IS is not "perfect" but limited in its usefulness and that is why we want a new one with 4 stops of IS.