Fungus (?) inside RF 70-200 F4 L

Started 3 months ago | Discussions thread
Karl_Guttag Senior Member • Posts: 1,152
Re: Fungus (?) inside RF 70-200 F4 L

Sinawang wrote:


I suspect the fungus is already with the dust and the dust got inside the lens then ended up on the front element and the suspected fungus eventually moving from the dust particle and spreading to the glass.

Here's after 24 hr I buried the lens with all the silica gel sachets I have while waiting my dry cabinet & UV light shipped.

From different angle you can see that kind of halo around the dust. It doesn't spread further as I worried. That's still the same size when I first saw it 2 days ago. The centre dot is the dust and there are another dust there in the back of the front element.

This stresses me out. The only relief is that it's not seen in the frame as it's outside the coverage area of the sensor.

I'll call canon today and see what I can get.

Please, don't get stress out. It is not that bad (yet).

First, ALL lenses have dust in them, and they will get more dust with time, even the best L lenses in the world. You can't have lenses that move in and out and seal against all dust. Also, note that waterproof is not the same as vapor proof. No lens is mold spore proof as mold spores are very tiny.

The good news is that if the dust and other imperfections are not near the sensor, they will not appear in the image. Note that even if the dust spot is on the sensor filter (just before the sensor), you can't see them until you stop down, generally to f16 or smaller. I don't think it happens today, but back when Canon used to say that a few bubbles in the glass were "normal" even for L lenses and would not degrade the image quality.

To a first approximation, all parts of the lens contribute to all parts of the image. So even if that mold spot were a black dot, you probably would not notice it even if you shot a picture of a white object. All the spot does is dim the whole image by the percentage of the light that is blocked (which is probably much less than 1%).

For a very simple but dramatic and simple example, see this video at the point linked to here:

Also, it appears that this is occurring on the outer part of the lens, which primarily contributes to the image only at the wider apertures so that it will be even more out of focus/invisible if it has any effect at all.

It is kind of like you scratched the outside of the lens. It does not make you feel good, but it is not hurting the image significantly.  Take some pictures of a white sheet of paper or some other uniform white object at various apertures and see if you can see it.

That said, since you live in a humid climate, you don't want it to get worse. You could get a nasty surprise someday when you put a lens out that you have not used for a long time. Also, mold can eat at the lens coatings and not be reversible via cleaning. You definitely want to take precautions regarding Humidity and UV light to kill/control the mold.

Even if you were to kill all the mold in the lens today, you would get more tomorrow. All lenses have microscopic mold spores in them. If they get water vapor, then they will grow. You have to keep the humidity down and kill them with UV (sunlight counts) light.

 Karl_Guttag's gear list:Karl_Guttag's gear list
Canon EOS R5 Canon RF 15-35mm F2.8L IS USM Canon RF 24-70mm F2.8L IS USM Canon RF 70-200mm F2.8L IS USM Canon RF 24-240mm F4-6.3 +13 more
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