Canon's lightweight L-series 400mm — f/5.6 without IS in the lightest possible L telephoto.
The Canon EF 400mm f/5.6L USM launched in 1993 as the lightest 400mm in Canon's L-series lineup — sacrificing IS and a stop of aperture for a dramatically smaller and lighter package than the 400mm f/2.8 or f/4 alternatives.
Optically very good — L-series quality at 400mm. The f/5.6 limits low-light use but the lightweight design makes handheld 400mm practical. Ring USM for fast, silent AF. No IS — the main compromise for the weight savings.
Canon EF mount with 77mm filter thread. Just 1250g — dramatically lighter than the 400mm f/4 DO at 2100g. L-series construction. Ring USM with FTM. 1.4x extender compatible for 560mm f/8. Minimum focus distance 350cm.
Available used at mid-range prices. The lightest way to get L-series 400mm — 1250g is remarkably light. No IS is the main drawback — handheld technique matters. For bird and wildlife photographers wanting light 400mm reach. A beloved lens with a devoted following.