In summary, the Canon EF 400mm f/2.8L IS III USM lens is a superb performer. You can view additional images in the Equipment Database, where you can add your own review, photos and product ratings.
[Dan K] had just such a lens from Sigma, but wanted to get it working fully with a camera using the Canon EF lens fitting. Hacking ensued. The lens in question was a Sigma 15-30mm f/3.5-4.5 EX DG ...
In terms of the Canon M10's ability to determine that it's properly focused when shooting the same target multiple times using the EF-M 15-45mm f/3.5-6.3 IS STM kit lens, its full autofocus ...