If you live in a dry, temperate climate, you're probably saying, "Lens what?" But if you're from one of those ghastly regions where the humidity will melt the headliner out of your car and turn your sun porch into a sauna, you know what we're talking about. Moisture trapped inside a camera can provide a healthy environment for foul fungus to grow, causing cloudiness and veiny patterns to form in the lens.
The best way to deal with lens fungus is to prevent it from taking hold, but even if it does creep in, your optics aren't necessarily doomed.
1. An ounce of prevention. Don't leave your camera sitting in a camera bag when you're not out shooting. Store it in a cool, dry place. If you're in an especially humid climate, keep your camera and lenses in an airtight container with some little bags of silica gel that will absorb moisture. Make sure to change the bags regularly so that you don't leave saturated silica gel sitting around with your gear.
If you go out shooting in the cold, wrap your camera in a plastic bag before bringing it into a warm room to prevent moisture from accumulating inside the camera.
2. A pound of cure. If it's too late for prevention, you'll have to have your lens cleaned. Otherwise, the fungus can affect image quality and eat into the coating on your optics. Don't rely on home remedies such as leaving your lens in the sun; they won't solve your problem.
We strongly recommend sending the camera to the manufacturer or taking it to a repair shop for a professional cleaning. However, if you're determined to do it yourself and are willing to risk doing serious damage to your camera, you can try taking the lens apart with a jeweler's screwdriver and cleaning it with a vinegar solution on a soft cloth. Fungus usually grows between the glass elements of the lens, not just on the front or rear surface, which means that you can't simply clean it off of the outer surfaces. You must disassemble the lens.