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.
From Lensrentals.com:
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
Canon EF 400mm f/2.8L IS III in stock at Adorama
The 70-200 was just white paint, I think we all knew this 400 was something altogether new.
I love Roger's wit.
And yet, they all have dust in them when we get them. :-) Every lens does, it's just whether you have a strong enough light to see it. Also we aren't working in a large factory with machines milling things, etc. While not a clean room, we have pretty good dust scrubbers where we work.
But yes, to some degree we change tactics during reassembly. We can be cavalier during disassembly: the pieces are all going to sit on a table for a while so they will all have dust on them when reassembly starts. The main reason that reassembly takes longer is every piece is cleaned as it's reinserted. It's not unusual, too, for Aaron to do a bit of disassembly during reassembly because he finds he missed a piece of dust or a smear on an element.
As a TMI aside, this is part of the reason I can no longer do the disassemblies myself. As I've gotten old my close vision isn't good enough to find the small bits of dust that Aaron sees easily. Bifocal jokes may start now.
Roger
Lens Rental is , obviously, a rental, not an official repair facility. They must be busy enough with their own stuff, without being asked to repair customer's warranty damages.