Im travelling to osaka next week, and planing to upgrade from my 20D to a 40D, i have with that one a 70-300 IS but i still feel a little short with the zoom and i cant decide between the 100-400 IS and the sigma 170-500 Any help here?thanks guysbest regardsArturo

..between the Canon 100-400L and the Sigma 170-500. This should be obvious on price alone. Some see the Sigma 50-500 (Bigma) as a less expensive 100-400 alternative, but the 170-500 is a much cheaper, poorer optically, and less solid lens all together. I wouldn't consider it if you can manage eithter the Bigma or 100-400 (preferably).