Lens fungus in Bangkok: prevent it, clean it or sell?

Fungus is a living growth that settles on the glass inside a lens and spreads slowly across it. It likes exactly what a tropical city offers: warmth, moisture and darkness. A lens that is used and aired regularly rarely gets it. A lens that lives in a closed bag in a humid room often does.

How to tell fungus from dust and haze

Take the lens off the camera, point a bright torch through it from the back, and look in from the front at an angle.

• Dust looks like separate small specks. Almost every lens has some, and it rarely shows in photos.
• Haze looks like a milky, even film across the glass. It lowers contrast.
• Fungus looks like fine threads, branching lines or small spots with "legs", often starting at the edge of an element.

The same torch check is how any careful buyer - including us - looks at a lens.

How to store gear so it does not start

• Keep it dry, not just clean. A dry cabinet is the common answer in Thailand. A cheaper route is an airtight box with silica gel that you replace or dry out when it is saturated.
• Do not set a dry cabinet as low as it will go. Very dry is not better for rubber and lubricants. Many photographers keep a cabinet somewhere in the middle range rather than the lowest setting; check what the cabinet maker recommends.
• Do not store it in the camera bag. Padded bags hold moisture. The bag is for carrying.
• Use it. Taking the lens out, zooming and focusing it, and letting air and light through it now and then is the simplest protection there is.
• Leaving an air-conditioned room? In Bangkok it is going from cold to hot that fogs glass. When you take a camera from a cold room out into the heat, keep it in its bag for a while so the condensation forms on the bag, not inside the lens.

Can it be cleaned?

Often, if it is caught early. Cleaning means opening the lens, so it is a job for a lens technician, not for a cotton bud and household cleaner. Two things decide whether it is worth it:

• How far it has gone. Fungus left for a long time can etch the lens coating, and that mark stays after cleaning.
• What the lens is worth. Ask for the cleaning price first and compare it with the value of the lens. On an inexpensive kit lens, the cleaning can cost more than the lens is worth.

As a precaution, many photographers keep a lens with fungus away from their other gear until it has been dealt with.

If you want to sell a lens with fungus

Say so up front. Fungus is one of the things checked on every lens - it will be found with a torch in a few seconds - and it does lower the price. Mentioning it at the start keeps the quote accurate and saves an awkward re-quote at the meeting. More on what moves a price in what actually decides a used camera's price.

Whether we can buy a particular lens with fungus depends on the lens and how bad it is, so we do not answer that with a general yes. Send a photo taken with a torch shining through the lens on LINE, with the lens name, and we will tell you honestly. Camera bodies are priced on the site - find your model and add lenses in the next step.