Roger Cicala performed a teardown of the Canon EF 100-400mm f/4.5-5.6L IS II USM and came away wondering, "Is this the best built lens ever?"
From the LensRentals Blog:
"For those two or three of you who don't like a little lens strip-tease I'll give you the quick summary: the build quality on this thing is amazing. I usually laugh when people describe a lens as 'built like a tank' because what I know is the lens they are describing has a thick, heavy outer metal shell filled with tiny delicate pieces that break and wear out with great frequency. But this lens is built like a tank inside and out.The fully illustrated article can be found on the LensRentals Blog....
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!"
B&H carries the Canon EF 100-400mm f/4.5-5.6L IS II USM lens.