Are "Weather Resistant" Lenses Fungus-Proof?

[BruceSD]

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Today, I'm putting a couple of old lenses that I own out into the bright sunshine to treat fungus that's inside these lenses. One of these lenses is a vintage Nikkor lens that is NOT weather resistant.

Over the years, I've owned many lenses that had fungus inside; but when I reflect back on them, I just realized that none of my fungus lenses were rated as being weather resistant.  None of the weather resistant lenses that I've owned ever had fungus inside of them.

Of course that's just my personal experience, but I would like to throw this out there and see what your experiences have been with fungus inside of lenses. Have you ever owned a "weather resistant" lens that had fungus in it?  Is it even possible for a weather resistant lens to get fungus inside of it?  Do you feel that if a lens is rated as being weather resistant that it is less likely to get fungus inside of it?

[Akira]

I think that a weather resistant lens is only "weather resistant" when it is mounted on the camera.  The area around the lens mount is not sealed anyway.  The rubber gasket around the lens only works when the lens is mounted on the camera.

So, if you leave the lens in the humid condition, it will suffer from the mold sooner or later.

[BruceSD]

I think that a weather resistant lens is only "weather resistant" when it is mounted on the camera.  The area around the lens mount is not sealed anyway.  The rubber gasket around the lens only works when the lens is mounted on the camera.

So, if you leave the lens in the humid condition, it will suffer from the mold sooner or later.

If one keeps a rear lens cap always attached to the lens when the lens is not on the camera, do you think that might help to keep humidity out of the lens?

[Akira]

If one keeps a rear lens cap always attached to the lens when the lens is not on the camera, do you think that might help to keep humidity out of the lens?

Frankly, I don't think so.  "Weather sealed" doesn't mean "airtight".  There will be intakes and outtakes of the air (with some moisture, according to the environment) when the lens is operated for focusing or zooming.

The best way to keep the lens mold-free is to use it, because the air inside the lens can be circulated and kept fresh.

[pluton]

If one keeps a rear lens cap always attached to the lens when the lens is not on the camera, do you think that might help to keep humidity out of the lens?

Not if you are sealing humid air inside the lens.  [Non-humid]air circulation and exposure to light are the best preventatives against mold growth.  For many who live in humid climates, this means a so-called 'dry cabinet' for general storage, especially during the humid season(s).
BTW, your lenses that have fungus may be able to be cleaned.  I recently was given a Nikon 50/1.2 AiS that had a huge orange fungus growth about 3 elements back from the front.  I cleaned it and the fungus had done no damage---which is not always the case.  A reasonably priced service shop can clean it for modest $.

[Darkslide]

If one keeps a rear lens cap always attached to the lens when the lens is not on the camera, do you think that might help to keep humidity out of the lens?

Perhaps I'm odd, but I simply can't imagine a situation where I don't have a rear lens cap on a lens which is not mounted on a camera body.

Do you store lenses without caps? I'm not thinking fungus here, more dust and rubbish which inevitably gets into ANYTHING unprotected.

The fungus issue (which I must say I've never experienced) is basically down to humid conditions, and rear lens cap or not, I can't imagine being able to prevent this without making efforts to dry/dehumidify the area in which the equipment is stored.

[Dogman]

Maybe I'm the luckiest photographer on the planet but I've never had a lens develop fungus.  This despite living in a humid area and, in the past with non-electronic gear, using lenses in heavy rain and being pretty haphazard about keeping them dry or storing them.  Now I have bought lenses with fungus but none I've owned has developed it.

And now I've created bad ju-ju and jinxed myself, I'm probably gonna discover all my lenses filled with mold in future months.

[pluton]

It's the climate and/or it's the storage.  I keep lenses in drawers in metal office-type cabinets which are not hermetically sealed in any way.  They are face-down with rear caps, and many have a clear filter always attached. A friend who lives nearby recently discovered some Nikon gear owned by his late father.  The lenses were wrapped up in sealed plastic sandwich bags, and had been stored that way for 5-10-20 years.  Of 4 lenses, one had fungus growth.