Roger at LensRentals.com has done a teardown of the brand new Canon EF 100-400 f/4.5-5.6L IS II and has come away very impressed.
I know I can’t really, without showing you dozens of other lenses, do a good job of impressing you with just how robustly engineered this lens is. I will say that the insides look more like what we’d expect to see in a 500mm f/4 or 600mm f/4 lens, rather than a telezoom. It’s by far the most heavily engineered zoom lens Aaron and I have ever seen; and we’ve seen the insides of dozens of lenses in this range.
Well done, Canon engineers, well done!