stsva wrote in post #17850450
The lens is supposed to be well-sealed if you have a filter on - we're looking at you to be the test case.
The lens can be no more sealed than your lungs. Zoom in the lens breathes in, zoom out the lens breathes out.
The "sealing" works like the skin and skull of your head, stops the rain making your brain wet.
Your lungs still breathe in humid air if you are in a humid environment.
For Kev's situation, I believe the real problem is not the humid air. It is changing from different temperatures quickly.
For this reason, if I'm on a road trip, I avoid using air con and try to keep the temps in the car roughly the same as outside.
For the same reason, I would avoid going from, for example, hot outside area into a cool cave, without using some method of slowing the temp change for camera gear.
Kev, while using your lens in the predicted environment, I believe "using the lens" is what prevents a problem, by using the lens it is being exposed to UV light, preventing mould. Similar to the way you can drive your car through the rainforest and don't expect mould to start growing inside your car. Hose the inside of your car, wind up windows and leave it in a dark garage and you'll soon have mould.
I have a dry cabinet at home to store my gear. Therefore for periods where it is not getting UV exposure the humidity is lowered to prevent mould.