Lens Fungus – It Can Ruin Your Camera Lenses
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by Don Rock
Besides user clumsiness, fungus is a cameras lens's worst enemy. No piece of glass is immune, and fungus etched elements are not as rare an occurrence as some claim. Under the right conditions, fungus can form and if left long enough, a lens will be rendered damaged beyond repair.
No Lens Is Immune
This is not something that only happens to old lenses found in grandpa's basement. Modern lenses from makers such as Nikon and Canon can develop major fungal issues too.
The damaging affects of fungus seems to depend on how long it has been growing inside the lens; yet the actual amount of time it takes to etch the glass is unknown. Regardless, no one really wants to wait around to find out!
Stopping Lens Fungus
Fungus itself can be wiped off fairly easily. There's no need for special mixtures of peroxide and ammonia and no need for Ponds Cold Cream (as I've read somewhere). Just a little 90 plus percent isopropyl alcohol applied to a Q-tip or micro-fiber cloth will do the trick. Unfortunately, it's not the fungus that's the problem; it's what this organism does to the glass while it's growing.
At some point, fungus releases or produces an acid that can permanently damage lens coatings and glass. There's no point in trying to explain the specifics of how the organism does this, just know that it does. The important thing is to realize that it has to be prevented and controlled if you value your gear.
Anytime a lens is exposed to damp or humid environments, fungus can be an issue. Microscopic fungal spores are everywhere, including your lens. All it takes is a little moisture, and if left long enough, the growth process starts.
While it's not always feasible to dry-out a damp or fogged lens immediately after use, it's important to do so when possible.
To prevent fungal growth in your camera lens, use the following tips:
- Wipe lens body/exterior after use; flannel cloths work well.
- Clean and dry glass surfaces after use.
- Allow damp or fogged lenses to dry before storing them.
- Store lenses with one or more silica gel/desiccant packs.
- Periodically check your lenses for fungus with a bright light.
If you find spots on either the inside barrel or a lens element, then it's time to take action.
At its early stages, fungus may show-up as a small white spot or a piece of fuzz. At this point it probably hasn't had enough time to do any damage. Once it has had time to mature, it can cover a whole element in a tiny, vein-like structure. At a mature stage, it's likely too late and the damage already done.
Hopefully, you catch fungus at early stage and can get the lens cleaned by a competent repair person. Disassembling a lens is not for everyone and can be very tricky to say the least. Lenses are like little puzzles and require a strong mechanical ability as well as special tools.
My point here is to control the situation by taking the lens to someone who can clean it and stop the fungus before it has a chance to do damage.
Buying Used Lenses with Fungus
When buying a used lens that has fungus, you never know how long the problem has been there. Yes, there's always a chance that the fungus has been there a short while and can simply be wiped off; but it's impossible to tell.
As you may have noticed, used lenses with fungus usually sell at a large discount; however, paying half the price for something that delivers sub-par image quality is not a good deal.
Below is a recent advertisement by a well-known retailer who deals with a lot of used gear. Even at a much discounted price, this Nikon 70-200mm would be best avoided unless you need it for parts. Chances are that the fungus has destroyed enough of the glass to render this lens practically useless.
I once thought that buying older, manual focus Nikon lenses with fungus would be a good money making opportunity. I thought all I had to do was clean them and resell for a nice profit. Unfortunately, it didn't work out because more often than not, the glass would be permanently etched.
Removing Etch Marks by Buffing or Polishing
You cannot simply remove etch marks with buffing or polishing. I've tried. Even-though the marks may only be a few microns deep, you'll end up changing the lens geometry slightly; thus leaving you with a lens that won't focus.
I once polished a fungus etched front element from a Nikon 50mm by hand. I started with a mixture of water and 1000 grit silicon carbide on the end of a Q-tip. Once the etch marks seemed gone (as well as the coating), I followed-up with cerium oxide – a fine red powder used to remove faint scratches in glass. When the lens appeared clear, I reassembled the 50mm and took some pictures. The resulting photos were ugly and out of focus with no way of bringing them in focus since the lens geometry changed a tiny bit. This was a $20 lens bought off EBay so no big loss; but it was a good learning experience!
Fungus has ruined some great glass over the years and will continue to do so. It's up to you to prevent and control fungus before it has a chance to ruin your favorite lens!