 filter from the front of the lens beforehand.
If you use a germicidal lamp, follow its instructions and do not directly look at it with your naked eyes.
When using sunlight, make sure that the lens does not focus the light onto something flammable behind it. And avoid overheating the lens by leaving it in direct sunlight for too long, as this can cause sticky aperture blades.
This method will not kill all fungus inside the lens. There will always be some spores left alive in the plastic/metal housing of the lens and other components where light does not reach. For that reason, it is important to use proper preventative measures to keep the fungus from reproliferating later on.
In more severe cases, the only option (if you still want to use the lens) is to open the lens up and thoroughly clean it. Doing this yourself is tricky, and generally the best option is to hire the services of a professional lens technician.
I have placed a short guide on how to clean fungus from a camera lens at home further down this page, but your results will vary on the amount of fungus present, the complexity of the lens and your technical skills. A modern-day zoom lens is significantly more complex than a prime lens from 30 years ago, for example.
To give you an idea of how tricky lens mold is to deal with; it is practically never covered under warranty and the service departments of Zeiss and Canon refuse to even accept lenses with fungus. Last time I checked, Sony and Nikon do offer cleaning for this problem, but do expect to pay a decent price.
As with many things, prevention is better than cure. When it comes to fungus in camera lenses, there is no exception. The best way to keep lenses clean is by keeping spore growth in check.
As we discussed above, the main factors that accelerate fungal growth are moisture, light and nutrients.
We can influence the amount of moisture and light our gear is exposed to (as I will explain in this section), but nutrients are outside of our control. Particles such as dust, lint and dirt will find their way into the lens regardless of what we do.
Temperature is technically a factor as well, but since the suitable temperature range for most fungi (10-35°C / 50-95°F) is the same as typical living/working conditions, there is not too much we can do about that.
Arguably the most important factor in fungal growth is moisture. Since we can control this both when shooting and when we store our lenses, this is the best place to start in preventing fungus in our camera equipment.
For reference, the official ZEISS guidelines recommend keeping lenses in a relative humidity of between 30% and 60%.
When shooting outdoors, keeping the camera body and lens dry can be challenging. In poor weather (rain/snow/etc) and other situations with splashing liquids, it is almost inevitable to end up with some drops on your gear.
Drizzle and mist can be dealt with relatively easily. Regularly wiping your camera and lens down during use is often enough to keep things dry enough.
Light rain is a bit more challenging. Holding your camera under your jacket or coat until you are ready to shoot and putting it back afterwards is a good solution to reduce exposure to moisture.
In moderate to heavy rain, or if you are not able to keep your camera under your coat, you will need something more, like a rain cover. These do a great job at protecting your camera from a continuous barrage of water.
Altura Photo Professional Camera Rain Cover for...
Any extra lenses or gear that you are not actively using is best carried in a waterproof camera backpack. To reduce the humidity of the air inside the backpack, I recommend using desiccant packets. These contain silica gel beads that absorb moisture from the air, creating a dry and safe space for your camera equipment.
Endurax Extra Large Camera Backpack Waterproof...
Dry & Dry 5 Gram [100 Packets] Premium Pure and...
The above covers actual liquids, but does not cover water vapor that lenses encounter in the outside air. Not much can be done against that during shooting, unfortunately.
Lenses typically exchange air with their surroundings when zooming and/or focusing. It is inevitable that water vapor comes along for the ride. Not even water sealed equipment can protect against this.
Because we can not avoid moist air in a lens while we use it, we must address this as soon as possible when we are done shooting and are preparing to store our gear.
After using a camera lens outdoors, especially in humid conditions, one of your first steps should be to remove the lens caps. This helps trapped moisture evaporate out of the lens.
If the lens is a zoom lens, you can also zoom in and out a couple of times to exchange the air inside the lens with drier air from the room.
The next step is to store the lens in proper conditions. Recommended is a dry (30-60% relative humidity) location. Ideally it would have ventilation or air flow, but this is not as important as the right humidity levels.
There are several popular ways in which people create a suitable environment for storing their lenses.
One of the easiest ways to create a storage solution for lenses is to take a transparent container, add desiccant to it, and place your equipment in it.
This setup removes moisture effectively, lets light through, is cheap, and is easy to set up. A clear food container and regular desiccant packets are basically all you need.
Rubbermaid Brilliance Food Storage Container, BPA...
This method does have downsides, however. Namely, there is no air ventilation, and it is easy to accidentally make the container too dry.
Camera lenses should not be kept under 30% humidity for long periods of time. This dries out the lens’s sealants and adhesives to the point where the lens is not able to function properly anymore.
If you decide to go down this route, it is best to use a simple humidity sensor to keep an eye on the humidity levels and adjust the amount of desiccant to keep the RH levels between 30% and 60%.
A better (but more expensive) option to store your camera lenses is in an electronic dry cabinet. These cabinets electronically control humidity levels and are designed to continuously keep your camera gear in safe conditions.
Devices like these are automated, so there is no need to manually renew desiccant or periodically check on the humidity inside. Simply put your lenses and other gear in after shooting, and any excess moisture will be drawn out and kept out.
The initial investment is higher than going with the budget DIY option, but it is still cheap compared to the price of camera lenses and the cost of replacing a moldy one. Especially if you live or work with camera lenses in a humid area, you can not go without one of these.
In controlling fungus, UV light exposure is easier to do than humidity regulation. Humidity needs to be controlled continuously, whereas exposing a lens to UV light only needs to be done once every couple months.
Camera lenses that are regularly used outdoors do not need any extra care, as occasionally seeing the light of day is enough to keep fungus spores in check.
Lenses that are stored most of the time, or those that are exclusively used indoors, can benefit from UV light to prevent mold growth. There are several methods you can use for this.
Periodically taking a lens outside (in daylight) and shooting with it goes a long way in preventing fungal growth.
This is not a valid option for everyone, however. Whether it be due to time restrictions, owning many (never too many!) lenses, living in an area with long dark winters, etc.
A valid alternative is to place your lenses in a window sill or a safe place outdoors for a while. Any place that has plenty of sunlight and does not have nosy children, pets or other animals roaming around will do.
The only thing you need to do is remove the lens caps, open the aperture as wide as possible and leave the lenses for a couple of hours. Of course, you will need to remove any UV filters beforehand.
I personally prefer doing this on a slightly overcast day, as it is a bit safer. There is less risk of lenses overheating and ending up with sticky aperture blades, and the sun also isn’t so bright that you risk focusing the sun onto the end cap or table and melt/burn it.
If you want to have more control, or be less dependent on the weather, a germicidal UV-C lamp will do the trick just as well. These emit light around the 524 nm wavelength, which does a great job at killing fungus spores, bacteria and other pathogens.
To use it, place your lenses around the lamp and remove any UV filters and end caps. Then turn the lamp on without looking at it and leave the area, because UV-C light is quite harmful for your eyes.
There are several things you should never do if you want to keep your camera gear clear of fungus.
Keeping lenses in humid (>70% RH) conditions for longer than a couple of days.
Storing lenses in darkness for long periods of time.
Blowing on lenses. For example, when you want to remove dust or fog the lens for cleaning. Not only does breath contain a lot of moisture, but it also can contain all kinds of microorganisms that would be more than happy to grow in your photography equipment. Instead of your breath, use a rocket air blaster for blowing and lens wipes for wiping purposes.
Permanently storing cameras or lenses in camera bags. The fabric of these bags is an excellent place for mold spores to settle and multiply. Obviously, camera bags are still an essential tool to use while on the go, but