Lensrentals.com has done something I've never seen before, and that's tearing down a working Canon super telephoto lens. In this case, it's the brand new EF 400mm f/2.8L IS III, the world's lightest 400mm f/2.8 lens.
An interesting bit of information that Roger and Aaron did get from the teardown, is that the EF 400mm f/2.8L IS III uses the same focusing motor as the RF 50mm f/1.2L.
This is a great teardown and not for the faint of gear heart.
Some things we were already aware of or assuming. The lens elements are moved towards the mount side of the lens. There are lots of optical adjustments like all Canon lenses. Despite being far lighter, it’s still very solidly built with a very strong frame, tons of big screws holding everything together, and no weak joints that we can see. It’s what we expected; Canon’s been building super telephotos for a long time.
There were some other, more interesting things. The spring-loaded adjustable collar collection is something of a mystery to us and will remain so until we can spend some days doing optical adjustments on one. The use of the same motor as the RF lens is very interesting in several ways. Only some more tear downs will tell us if this is just a superior motor type that Canon is going to use in all electrically focused lenses (I suspect this is probably the case), or just in lenses with a lot of glass in the focusing element (another likely thing). Read the full article