Canon's original L-series 400mm f/2.8 supertelephoto — a massive professional prime for sports and wildlife.
The Canon EF 400mm f/2.8L IS USM is the professional flagship super-telephoto prime for Canon EF full-frame bodies. Three versions were produced: Mk I (1999, ~5,370g), Mk II (2011, ~3,850g, 4-stop IS), and Mk III (2018, ~2,840g, 4-stop IS). The Mk II — most common on the used market — uses a drop-in 52mm filter holder. L-series weather sealing. Sixteen elements in 12 groups (Mk II).
Mk II specifications: 16 elements in 12 groups (2 fluorite + 2 super UD elements). Drop-in 52mm filter holder. 3,850g. 4-stop IS (Normal and Active modes). Ring USM provides fast, quiet AF. L-series weather sealing. Tripod collar. f/2.8 maximum aperture. Compatible with Canon 1.4x and 2x TC-II/III teleconverters.
The 400mm f/2.8 is the primary super-telephoto for sports, wildlife, and press photography: f/2.8 at 400mm provides the fastest effective aperture for action stopping at extreme distances. The Mk II's 3,850g versus the Mk I's 5,370g was a landmark weight reduction enabled by fluorite elements. Identify version by weight: ~5.4kg = Mk I, ~3.85kg = Mk II, ~2.84kg = Mk III.
On the used market the Canon EF 400mm f/2.8L IS USM is available at professional super-telephoto pricing. Condition checks: IS engagement, ring USM AF response, drop-in filter holder condition, tripod collar rotation, and L-series sealing. Confirm version by weight. Compatible with all Canon EOS EF bodies; on RF bodies via EF-RF adapter.