Thanks Alan for all your comments and posts on this lens. I received mine yesterday and though haven't had much chance to use it yet, my initial impression is that this is indeed a great lens to have. Lenses like the EF 100-400 II and the RF 100-500 are a bit beyond my budget, so a while ago I bought the Sigma contemporary 100-400mm. I tried two copies of that lens actually and sold them both as they seemed quite soft at 400mm. This new Canon lens is sharper, considerably lighter and cheaper. Maybe I just had bad copies of the Sigma, but even if the IQ was equal, the weight difference makes the Canon the far better choice in my opinion.Now I have had the lens for 3 weeks, I think every one should have one! I've worked my way through an EF 100-400mm, EF 100-400mm II, Tamron 100-400mm f/6.3 (and tried out the Sigma version), Tamron 150-600mm, Sigma 150-600mm C, RF 100-500mm and now the RF 100-400mm. The best is the 100-500mm. The most fun is the RF 100-400mm, and it beats into the ground the Tamron and Sigma 100-400mms for AF, and it's pretty close to the 100-400mm II in the centre for IQ. It's a steal.