Fujinon XF 100-400mm is very interestingly constructed lens due to its Weather Resistance. I’m curious enough to check how is it protected from dust/moisture in the rear area where the vent openings are located. Zoom from 100mm to 400mm involves large volume of air to move in, and rear lens element is also moving. This explorative disassembly sheds some light there.XF 100-400mm is also a heavy lens, so mount ring is secured with four bolts tighened quite hard. Initial short angle rotation torque required to unscrew them. Then I also unscrew black bolts on the inner plastic ring and pull it out to release lens contacts. After that I remove the mount ring.
Next step is to unscrew four black bolts holding the ring with control switches, then disconnect the ribbon cable and pull out that ring.
It is relatively easy procedure, so technically it’s simple to replace this ring or repair/clean switches if required. On the opposite side of the ring some air filter is located preventing dust or water drops to go inside.
So looks like when lens is zooming in/out the rear element is moving inside. Fuji engineers put wide rubber ring around rear lens module.
Note – there are four shim rings located under every mount bolt, so don’t forget to put them to same locations during assembly.
When you zoom XF 100-400mm lens the air in camera mount chamber is moving inside/outside through air filter in the bottom area of control switches ring, and rubber ring sealing around rear lens group does not allow that air to go inside where the aperture and OIS modules are located.
There are plenty of ribbon cables organized around the rear lens inner frame. They are connecting: OIS module, AF drive, Zoom sensor, Focus ring sensor, Aperture control and sensors.
Technically if air filter fails to stop water, it may spread up to that cables and cause significant damage. So it’s important to not zoom the lens if the water is located at ventilation openings.
I finished explorations at this step and assembled the lens. Fuji did great job sealing the rear area.