The Curse of Lens Fungus

Nikkor AF-S 300 f/2.8 G ED VRII

Fungus - the term likely to cause fear for any enthusiast photographer. Fungus in a lens is something that all photographers try to avoid. This is something that is almost impossible though because fungal spores are everywhere, from the air we breath to every surface that we touch. The best we can do it to stop them from germinating.

Dust and moisture can form inside any camera lens, even fully weathersealed optics during storage, use and mounting/unmounting from the camera. If the dust contains these fungal spores these can grow within the lens. The fungal spores are microscopic but what you can see are it’s tendrils. These tendrils spread out to gather nutrients for growth and when all the nutrients. Dust and moisture are consumed as the tendrils spread,, leaving behind etchings in the delicate coatings on the individual lens elements.. If there are sufficient nutrients the fungus forms spores to grow the next generation of fungus and so on.

When that happens, the lens will show a reduction in contrast where the fungus damage is most present, and they may exhibit fringing or flaring.  Overall, the decreased image quality can ruin the images from a particular lens.

I had always assumed that fungal damage (including mould) was something that only happened in hot humid climates and would not be a problem in the UK. This assumption was turned on its head when my most expensive optic was diagnosed as having a fungal infection!

As I have previously discussed, I have moved from Nikon DSLRs to their mirrorless Z system and have sold most of my F-mount lenses to offset some of the costs for switching to the Z-mount equivalent lenses. I kept two F-mount lenses, the excellent AF-S 300mm f/2.8 G ED VRII and AF-S 500mm f/5.6 PF ED VR lenses. Medical issues meant that I was restricted in the weight of equipment I could carry so the 300mm, FTZ adapter and Nikon Z7 ii combination at almost 4kg was getting to be a bit uncomfortable to use for any length of time.

Although this was a stunning lens, and extremely expensive, it was sitting in my camera bag and never getting used - I had taken less than 100 images using the lens in the three years since buying it, so I made the difficult decision to part with it. I contacted WEX Photo Video for a part exchange price and sent the lens off for assessment. After a few days I received an email informing me that the lens was showing signs of fungus/mould growth on some of its internal elements. Given the little use it was difficult to understand how this could happen.

Looking back, the last time I used the lens was during a cold damp winter in northern England. I remember using the lens to take some bird shots and then returning to the car, taking the lens off the camera and putting it in its case. This was then taken into the house and stored under my desk for almost 2 years due to my health issues. Fungus loves warm dark and moist places so I can only assume that the cold lens started to form condensation in the warm car and this provided the moisture for the mould to grow. The lack of use meant that the lens was effectively stored in its damp environment without being exposed to fresh air and light.

I agreed to have the lens cleaned before they would trade it in. Inspection of the lens provided a quotation of just over £500 for it to be disassembled, cleaned, rebuilt and calibrated. Although expensive this was a fraction of the trade in value of the lens so I proceeded with the repair and sale of the lens.

The lesson to be learnt is to ensure that lenses are cleaned, dried and regularly used to prevent mould and fungus from growing. If I had let the lens dry out before storing in its case this might not have happened. The fungus spores may have been present in the lens when it was bought or infected during the little use it saw.

I am now more careful with lens storage. I regularly clean the lenses with a microfibre cloth and blow any dust from the exposed surfaces with a rocket blower.. If the lenses are used in cold damp environments I allow for them to warm up before cleaning and putting into the camera bag. I haven’t gone to the trouble of sealing lenses in plastic bags to prevent condensation as they warm up at this stage but if exposed to cold weather for any length of time it is something to consider. I also keep an eye on the humidity inside my camera bag using a small electronic hygrometer that links to my phone via bluetooth. So far relative humidity levels in the room the camera equipment is stored tends to vary between 40 and 60%.. (A RH of less than 35% may also cause trouble as it tends to dry out seals and lubricants within the lens).

The only way to avoid this happening again is not to allow the spores to germinate by depriving them of the nutrients and other conditions essential for them to thrive. Internet searches suggest that mould / fungus becomes a problem under the following conditions:

• dark

• warm

• dust or grease (including fingerprint grease and actual lens lubrication)

• relative humidity of greater than 70% for three days or more.

By using the lens and keeping it clean and trying to maintain a relative humidity of less than 60% you can reduce the chances of fungus occurring.

If is does happen, however, there are companies that can clean and refurbish your lens for a reasonable cost. For cheaper lenses it may be more cost effective to purchase a new (or preowned) lens but in the case of more exotic or expensive lenses repair can be a worthwhile investment - the lens is cleaned, serviced and recalibrated at the same time as the fungus being removed.