Fungi in photographic lenses

Can This Affect Me?

SLR lenses are expensive and are often used in damp environments where spores of fungi can enter the lens and under favourable conditions, start to develop. While this is also true for compact cameras, these are both harder to check and cheaper to replace, thus are not discussed here.

Anyone who cares about one's equipment thould regularly check the lenses for fungal infection. This can be done easily by looking through the lense towards a uniform background (eg white paper). Make sure the aperture is wide open. With some lens mounts this may mean moving a lever, or even mounting the lens on a camera and looking into the front of the lens. If what you see even remotely resembles the image just below, you may be in a serious trouble.

The above image was taken of a Canon 70-210mm zoom lens, which I had a chance to observe while helping a friend to purchase a used camera. Due to the way the diaphragm of the lens operates, it is wide open only when the lens is mounted on the camera. Therefore, the owner of the lens did not have any idea that there was someone living inside the lens.

Upon further investigation, it became clear that the particular lens was badly infested. Several glass surfaces were affected, some of them pretty seriously.

The lower side of the image is dark because of vignetting of the light which I shined in through the viewfinder. The darkness on the right hand side, however, is at least partially caused by fungus on another lens surface.

Does it affect Image Quality?

In its early stages, fungus as seen above does not show up on the photos. It is actually pretty dark, and since images of no lens surfaces appear on your picture, you will never get an image like the ones above by accident. The fungus usually starts its life in the dust and organic materials in the lens barrel, and no visible effects may be seen for years. Once it reaches out onto the glass surface, it will slowly cover it with a mesh of lines. The first effect is probably very slight loss of image brightness, followed by increased flare from light reflecting off the growth. In its final stages, the lens surface may become etched by the chemicals excreted by the fungus, at which point image sharpness becomes affected. You will probably be able to use the lens for several years before it reaches this stage. Once you get there, you will need to have the lens cleaned, or replace the lens.

How to Avoid Fungus?

There is no recipe which would give you 100% guarantee that you will never get fungus in your lens. The following suggestions may reduce your risk, however.

Keep your lenses in a dry, cool place. If you use your equipment in damp environments, let it dry as soon as you return into a drier room. Never leave your equipment in a closed (splashproof) camera bag when it need not be there. Leather lens cases are known to be especially bad, because leather is a natural product where fungi can grow before they proceed on to the lens. Synthetic materials are better, but they give no guarantee either.

If your lens changes its length when focusing or zooming (most lenses do), outside air is sucked in when using the lens. If you come in from moist environment and just leave the lenses lying around, it will take days before the moisture inside the lens drops to ambient levels. You might zoom the lens back and forth several times in a dry room before putting them away, to replace some of the air inside.

If you store the equipment in a sealed (airtight) case, adding a small bag of silica gel or other absorbent may help. You will need to monitor its status (usually a change in color of an additive) regularly. As soon as the gel shows signs of saturation with water, it should be replaced or dried. Otherwise the process will reverse, and instead of drying the case, it will add moisture to the air and make things worse. For the same reason I would recommend against water absorbers in any situation where the container is not sealed airtight.

Several people have asked me about the best relative humidity to keep their lenses at. I have not seen any hard data on this, but anything below 50% should be reasonably safe. If you go below 30%, the lubricants in the lenses (diaphragm, focus, zoom mechanisms) might dry out faster than you like. The best temperature would probably be around 20 degrees C (68F).

What Can I Do to Remove the Fungus?

Once it is there, there is very little you can do yourself. You may slow down or stop the growth by following advice from the previous section. I have heard suggestions of using ultraviolet radiation (sun rays) to kill it, but since parts of the growth are outside of the glass area, this is probably only a temporary solution. Some types of glass are not transparent to parts or the whole of ultraviolet spectrum, and the radiation will be absorbed before ever reaching the fungus. As a chemist, I have also thought of poisonous gases, but (1) they may kill you before they kill the the fungus, and (2) they may corrode the mechanics of the lens, so better do not try this.

Taking the lens apart and cleaning it may be an option. One reader of this page, Chris Sherlock, has reported that he successfully

[...] cleaned fungus from my wifes OM1 zoom lens from an internal lens surface with Methylated spirits and it disappeared without a trace. He had to dismantle the lens, for which training as a camera tech several years ago was a handy skill to have. He further wrote: Taking lenses apart does need prior experience or a repair manual. For those who have neither perhaps the best way is to leave the job to someone who does! [...] What I really meant to say was don't write off the lens/camera as useless until an attempt at cleaning has been made.

In warmer and moister areas of the world, professional lens cleaning is a service routinely offered by the camera repair shops. Kelvin Lee from Singapore wrote that it costs between approx. US$10 (small primes like a 50/1.8) and US$80 (the bigger zooms) to have a lens cleaned (these prices only apply to Singapore; other parts of the world would probably be higher). Even if you live further north, calling the local repair facilities appears to be a good idea.

Another suggestion from Singapore comes from Edward Au. He wrote:

[...] purchase an automatic dryer cabinet. I bought a Japanese made dryer cabinet of about 68 litres in volume which costed me about US$350. A Taiwanese made would cost much less. The dryer cabinet is fully automatic, just plug it into a power outlet and it regulates the internal humidity down to about 45% (adjustable, but it will take some number of hours to achieve this). Beware of the input power when purchasing one. The manual says it is available in either 110VAC or 220VAC. In Singapore, only 220VAC models are available.

Btw, the dryer only helps preventing and protecting your equipment, it won't heal if your equipment is already infected.

A failure story by Hoo Yuen Chong, also from Singapore, talks about using a

[...] UV lamp. By that I mean those that are of the shorter wavelength type that can harm the eyes and are used in the electronic industry. I once used one such lamp about 15cm long (battery operated 5W) to shine on a 50mm f1.4 lens for 48 hours. After that I noticed, not only the fungus didnt go away but it continued to grow.

Some additional price information comes from Sergio Denys from Brazil (June 1997):

For your information: Here in Brazil I had my Canon lenses cleaned for US$35 (50mm), US$75 (35-70mm) and US$85 (70-210mm) in an authorized repair shop. By the way, the service is not guaranteed by the shop because some residual fungus may remain in the lenses. One of my lenses could not be completely cleaned and is definitely damaged.

Comment submitted by Tom Resident (aquatom@pacbell.net, March 1998):

On my lens (15mm/3.5 Nikkor) it look very different than the pictures on your web page. It look like a circular fog on the outer edge of the front element. Completely colorless, the coating of the lens just lost its gloss. This all around the front element!

You can prevent its growth by exposing your lenses to direct sunlight, No this won't damage them! The UV rays actually kills any fungus growing on your lens, but it wont clean any damage. This is only good for the front element, which is most often attacked by the pest. Just by keeping your lenses in a dry environment, won't necesarily prevent the growth of fungus, (I live in California).

No, you cannot clean the damage done by the fungus! If you can clean it, than it wasn't fungus. Only way of repairing the damage is to replace or repolish the glass afected by it, because it actually eats up the coating of the lens.

Comment submitted by Bill Lady (May 1998):

In my experience, lens fungus is unpredictable:

I purchased three new SMC Tacumar lenses at the same time some years ago. I still have them. The F 1.4-50mm normal lens has so much fungus in it that it is unusable. A local (Florida) camera shop offered to send it away for cleaning, at a price of $74.00, but I decided to buy an identical used lens instead. The other two lenses, a telephoto and a wide angle, are still in perfect condition. They have all been kept together in the same camera case since purchased, and always used and stored under identical conditions. There is no logical explanation for the difference.

Rick Oleson wrote in August 1998:

I have had both successes and failures. The first infected lens I dealt with was badly etched so that it was optically bad after cleaning; from this I assumed that fungus would always be unrecoverable and avoided lenses with any trace of it. More recently I have encountered some that have looked very bad but had not etched the glass and cleaned up very well. So far I have not figured out a way to tell the repairable ones from the hopeless without taking them apart and cleaning them.

If it isn't etched, getting the fungus off the glass isn't hard. In addition to regular glass cleaner I use naphtha to clean camera parts as it evaporates well, is an effective solvent but does not attack plastic. However, you have to be very careful with lens coatings, especially older ones. The real trick is that it's going to be very difficult to get every trace out of the barrel, and eventually it can grow back. Once a lens has had fungus and been cleaned, I would check it often and assume that repeat cleanings will probably be necessary to keep it from doing damage.

Doing this yourself is difficult, especially since every lens seems to be built differently even when you use only one brand. And in the case of a zoom it's extremely tricky.

The best way to deal with fungus is to avoid it.

An interesting experience submitted by Marc Falcone in November 1998:

I have bought a second hand 110-160mm zoom for a rollei 6x6 projector. When I opened it for cleaning, a internal divergent piece fall to the ground and broke in two pieces. I had the idea to go to an optical (ordinary eyeglass) shop, and asked if they were able to order a copy of this piece. I asked them that it must be made of same glass quality, same thickness, same dimensions and same diffraction.

After a week, I got my new piece for the price of an ordinary eyeglass piece (less than US$ 40). I mounted back my lens and I tried it. I were unable to discern any loss of sharpness or of other qualities.

Disclaimer

The information on this page has been gathered from various sources on the Internet, and from personal experience. I am not a biologist. I will assume no responsibility for results of using or misusing the information provided.

Technical details of taking the pictures on this page.

The infected lens was mounted on a camera on tabletop tripod, angled up. A white piece of paper was placed on the table behind the viewfinder and lighted by a household lamp (60W). The picture-taking camera was equipped with Canon EF 28-105mm lens at 105mm, f/8.0 and Nikon 6T (3 diopter) close-up lens and mounted on another tripod just next to the table. Autofocus was not able to find the fungus, so manual focus was used. Exposure was bracketed +/- 2 stops from the meter reading, but the final prints (Kodak Gold 400 film) were almost indistinguishable. Prints were scanned in a 600dpi flatbed scanner, cropped and edited with Corel PhotoPaint and xv.