To be honest, I'm not particularly interested in this lens as the Canon EF 100-400 f/4-5.6 L IS is not one of Canon"s better zoom. However, the early review seems to be quite good. If I'm considering upgrading the 500mm f/4 MK 1, this pretty much gives me more focal length at the expense of 1 stop, albeit at half a kilogram weight premium. I think I can also permanently retire the 400mm f/2.8 L IS too. Getting old. Lighter is better.