[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 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.
(From Canon lens literature) Designed to satisfy the discriminating needs of sports and wildlife photographers, the EF 200–400mm f/4L IS USM Extender 1.4X is a high-performance super telephoto ...
The Canon 6D is available body-only, or bundled with the EF 24-105mm f/4L IS USM "kit" lens. The test images shown on most other pages of this review were taken with very sharp references lenses ...