What is lens fungus? (and what can I do to fix it?)

I recently picked up a really cool camera for $10 at the flea market. The transaction was so quick, that I didn’t even have the chance to test it. Turns out, that lens has a pretty bad fungal infection. 

How bad is it to have mold or fungus in your lens? 

A fungal infection inside a lens will slowly ruin image quality as it grows, significantly reducing resale value. Even if the fungus is killed with UV light, it may persist and spread inside the lens. Often if one lens has fungus inside, other cameras or lenses stored in the same conditions will also contain some amount of fungus as well. 

A mold or fungal infection in your lens isn’t exactly a death sentence. The camera will continue to function and it may even take years before you notice a reduction in image quality. 

However, it’s always better to fix the problem sooner rather than later. Over time, that fungal or mold infection will worsen. If you find some of your equipment is becoming moldy, the problem may be starting from your equipment’s storage conditions.   

How to identify a mold or fungal infection in your camera lens? 

Fungus and mold have a very particular pattern when compared to dust. Dust will simply appear as dots inside of the lens. But mold and fungus will branch out. 

The easiest way to find out if there is mold is to ensure the lens aperture is completely open, and to then shine a light from your phone through the lens. If your lens has a leaf shutter, open the shutter with bulb mode and shine the light through the front element. 

Avoid looking directly into the light — especially with a zoom lens — as this could hurt your eyes. Try to look at the back of the lens from the side. The light will illuminate any dust, scratches, mold, and haze on the lens. 

You can tell it’s fungus or mold if there are little branches extending from the middle. The longer the mold has been active, the longer the lines coming out from it will be. 

If you see anything similar to this when looking at a used camera, put it back. It’s simply not worth the hassle — no matter how good of a deal the camera may be. 

What is the problem with lens fungus or mold?

Mold or fungus will continue to grow inside your lens and eat away at their coatings. When that happens, the lens will show a reduction in contrast where the mold is most present, and the may also exhibit fringing or flaring. 

Overall, the decreased image quality can ruin the fun of using a particular lens. Bad flaring means it will no longer be good for capturing subject backlit, as the flares will reduce the contrast around the edges.

The lens coatings are also important for reducing color fringing, or chromatic aberration. Color fringing makes images appear less sharp on high contrast edges, because the color spectrums are separating instead of hitting the film at the same point. 

Some of these problems can be fixed in Photoshop, but overall they’re impossible to fix in the darkroom. Some photographers will use an unsharp mask in the darkroom to reintroduce sharpness, but that is a difficult process to master.   

Mold will also reduce the resale value of any camera or lens that it affects. Taking a quick look on eBay, the cameras or lenses with even a small spot of mold or fungus will immediately be valued 20-40% lower than clean copies. If you’re an honest seller, you will have trouble getting rid of a fungus-y lens. 

How does fungus grow inside a lens? 

Even in the most inhospitable locations, life always finds a way.

Mold gets into the lens via dust particles in the air. And the tiny bit of moisture, and nutrients inside the lens is enough to keep it alive and slowly spreading. It makes its way inside when zooming or focusing with the lens when the moving elements create a small vacuum that drags dust and spores inside. 

Fungus and mold are usually found in cameras that were stored in humid climates. Cameras purchased from South East Asia and Japan are particularly prone to mold if they were stored outside of a dehumidified cabinet. 

That said, any rainy, damp, or cold climate can also provide moisture for lens fungus to grow. It is important to always wipe down any condensation that forms on your camera equipment when bringing it inside from a cool walk or hike.

How can you get rid of mold or fungus?

Getting rid of mold is no easy task. In general, mold is easy to kill temporarily using UVC Light or by gently cleaning it with hydrogen peroxide — so long as you’re willing to disassemble the lens. 

If you do plan to disassemble the lens, ensure that you have a large, clean working space. Keep everything in the order you took it apart, and don’t lose any small screws. 

When cleaning the elements, be sure not to damage them by rubbing too hard, or using too strong of a hydrogen peroxide solution. If the mold is tough, you can dip the elements in the solution for a half-hour, but be sure to fully clean the solution off so that it doesn’t slowly ruin the lens coatings. 

If you’re not comfortable taking on this task, then the best move may be to take your camera or lens in for service. Otherwise, it’s usually possible to purchase a broken parts camera fairly cheaply to practice with.

Using a UV light to kill fungus in a lens

UV, or ultraviolet light can be a useful tool for killing fungus and bacteria. The sun naturally emits some UV light, which can kill fungus and mold with a week or a months’ worth of exposure. But if you want quick results, or live in an overwhelmingly overcast climate like the Pacific Northwest, the next best solution may be to purchase a UV light. 

But not all UV lights are made equal. Most commercially available UV pens don’t produce a low-enough band of light, making them virtually useless against bacteria and mold. The ones that actually work (and are used in hospitals and other medical institutions) utilize the UVC spectrum instead of just UV. 

UVC has a spectrum between 200 and 280 nanometers (nm). But the most common UV lights on the market typically use 365-380nm, which means they’ll be ineffective at killing the fungus inside your lens, even over a long period of exposure. 

The flashlight guy tested one UVC light by Fenix, which purportedly has a 280nm LED light that has been shown to kill 99% of bacteria in lab tests. If it’s used close enough to the lens surface for a long enough time (with adequate protection), it should be enough to kill the fungus. But I would only recommend rushing out to purchase one of these if the fungal infection is new.

For more information on UVC lights, take a look at this article by the CDC, where most of the safety and efficacy information published on UVC lights is sourced from. This article, published by Regency Lighting, contains a useful infographic on the different spectrums of UV light and their uses.

It’s difficult to source flashlights that emit UVC wavelengths. There are cheap light bulbs available that shoot out 250 nm wavelengths and will fit into a regular socket, but users can’t be in the room when those lights are shining, or they risk sunburns and severe damage to their eyes. In the end, it’s difficult to suggest a UV light as the best solution. Even if it does work, the dead mold or fungus will still be in the lens, and some living parts may even be protected inside the guts of the camera body itself. 

How to prevent mold from forming in the first place

The best offense against growing mold colonies on your equipment is defense. 

Mold loves 3 things: water, dust, and oil from your fingerprints. Keep the lens clean and dry to prevent mold from forming in the first place. 

If you come in from the rain, clean your camera gear with an antiseptic wipe, and ensure it’s as dry as possible. Silica is your best friend if anything gets wet. I personally keep a bag of silica packs, like this one from Amazon, around for this exact purpose (it’s also saved my cellphone on a few occasions).

Avoid touching the front and back elements of your camera lenses, and clean it promptly when you do. That will reduce the chance mold has to start growing on your lens in the first place. 

But the very best thing you can do is fix the problem as soon as you see it. 

If the mold is already growing, then the best thing you can do is to stop it in its tracks by shining a UVC light through the lens. Just be aware that these lights can damage your skin and eyes, so protective glasses and clothing should be used at all times. 

Final thoughts

If you see a camera or lens that has mold or fungus, just pass it up. It doesn’t matter how good of a deal the camera or lens may be. Mold or fungus is not worth the hassle. It ruins image quality, significantly hurts resale value, and can even get inside your other camera bodies and lenses. 

All in all, it’s not worth the hassle — unless you really like cleaning, and want to learn how to do camera repair on a cheaper body. And if you’d like to learn more about film camera body issues, take a look at this article I wrote on the top 5 issues to check on a film camera before buying it.

Have you ever dealt with a fungus-y lens or camera? Let me know your story down in the description below! Or, make a post about it in the Learn Film Photography official Facebook group and Instagram account — I always love hearing your stories.