When a lens is specified as "weather sealed" it means that the lens will be somewhat resistant to external sources of things such as water and dust only when both the lens and camera are "weather sealed" and the lens is attached to the camera. "Weather resistant" never means "water proof" or "hermetically sealed." If a camera or lens is actually airtight, the manufacturer will loudly proclaim that it is waterproof, not weather sealed or weather resistant.
It also does not mean that the lens is isolated from the internal parts of the camera, such as the camera's light box. There is no barrier between the back of most lenses and the light box of most cameras. Air is usually free to move between the light box and the lens. Since fungi spread via airborne spores, it is entirely possible that placing a "weather sealed" lens on a body with fungus will allow it to spread to the lens. It is also likely that your lens already has a few fungus spores in it, along with dust.
The key to preventing fungus issues in camera gear is not in preventing fungal spores from getting into it. Fungal spores are everywhere on Planet Earth. The key is to not provide the conditions that encourage growth of fungi:
- Lack of UV light (such as unfiltered sunlight)¹
- Warm temperatures
¹ Yet another argument against always having a UV filter on the front of a lens for "protection" - you're "protecting" the fungal spores inside your lens from the sunlight that kills them.
Roger Cicala, the founder and chief lens guru at lensrentals.com, has often waxed eloquent regarding his disdain for camera manufacturers that claim "weather sealing" while refusing to cover water damage of any kind under warranty.
Removing a Fly from ‘Weather Sealed’ Canon 70-200mm f/2.8L IS II
How to Ruin Your (or Our) Gear in 5 Minutes (Without Water)
From Lensrentals’ Canon 5D Mk IV Teardown:
And, of course, as with every camera ever made throughout history, this one has ‘improved weather sealing’. It’s not improved enough for the warranty to cover water damage, of course, but still, that’s worth a look.
OK, as you all know I don’t take cameras out in the rain without plastic covers. Because we write off ‘weather resistant’ cameras for water damage every week. But I know you young people live life in the fast lane and like to take risks.
From the blog entry About Getting Your Camera Wet… Teardown of a Salty Sony A7sII:
Here’s a list of bad things that we’ll discuss.
- Camera manufacturers market their equipment as weather resistant. But if you get water inside the camera the warranty is void. So that’s pretty much “we guarantee it will work unless it breaks.”
- People think weather resistant means waterproof because they want to believe that.
- Service Centers play the impact/moisture damage card so much that everyone assumes they are full of …shirt… when they say so.
- There are two kinds of photographers: Those who have ruined a camera from water damage and are careful about water and see #2.
- Most service centers won’t work on a water damaged camera, even if you pay them. Some won’t even open it up to look inside if they see evidence on the outside.
Later in the same blog:
Trusting ‘weather resistance’ is risky business.
They all say they have it. But none of them define what it is or how much they have. This camera had easy water access from the battery door, the entire bottom, and around the camera strap lugs that we showed you. It also has two rotating dials that you can pour water through, but this splash didn’t hit those. The viewfinder and hot shoe are a bit leaky, too.