This rather “elite” lens with a price tag of $78,000 is used by broadcast or movie crews which needs to have a very long zoom (20X) capability, which can further be extended to 1500mm with the built-in 1.5X extender. This is a dream lens for people who want to shoot 4K movies while staying at a good distance from the subject. Sports, racing or wildlife movie capture are obvious examples, but the possibilities are endless.
It would typically be mounted on a Canon C-Series “cinema” camera, but some users also use it on a $10,000 EOS 1D DSLR camera. In theory, it could mount on a more modest model, but if you can afford the lens, we’ll just assume that you don’t have a EOS 60D… I won’t own one anytime soon, but it was a beauty look look at and play with on the show floor.