That’s not fungus on your sensor – It’s glass corrosion

Fungus is a well-known issue in photography gear. Typically, however, it’s on older equipment. Film gear that’s been sitting in a box in the basement for the last couple of decades. But sometimes, what you think is fungus isn’t actually fungus but glass corrosion.

In this video from Kolari Vision, we learn what glass corrosion is and why some cameras from companies like Leica and Blackmagic are affected by it while others are not.

What is glass corrosion?

Glass corrosion is exactly how it sounds. While we might thing of glass as being inert, not all glass is created equally. This is especially true when it comes to optical glass. Some glass can actually absorb moisture from the air, and this leads to oxidation.

It begins with microscopic fractures, but over time, it can become very obvious. And we’re not just talking about how it affects the images, but that you can literally see it with your eyes when looking at the sensor. It looks a lot like fungus, but it’s not.

It’s similar to rust on iron and steel. And just like iron and steel, glass can actually be protected from this oxidation.

It’s been well-known in Leica for years, with complaints about sensor corrosion in the Leica M9 going back as far as 2014 – only five years after the camera was released. In 2020, Leica removed the option of replacing damaged sensors, making you buy a whole new camera instead.

How to stop it?

Stopping sensor glass corrosion happens at the manufacturer level. Typically, it’s done by coating the surface of the glass or sandwiching it between glass with a chemical makeup that doesn’t oxidise. Other than storing your equipment in a low-humidity environment, there’s not really much you can do yourself to prevent it.

The other way to prevent it is to simply use a type of glass that isn’t prone to corrosion. As shown in the video above, the hot mirror from a Nikon D70 DSLR, a twenty-year-old camera, suffers from no corrosion whatsoever. Other cameras, like more recent Blackmagic and Leica cameras can show corrosion very quickly.

Of course, that decision is out of your hands. It was made before the first cameras had even rolled off the production line. So, all you can really do is get yourself a dehumidifier or a storage cabinet that extracts moisture from the air to keep humidity low.

Can it be fixed?

Once corrosion happens, the best solution is to polish off the top layer and reapply the coatings. But this isn’t exactly something you can do at home. Kolari is able to solve this issue for Leica and Blackmagic owners by replacing the hot mirror, which is what this video is really about.

That is technically something you can do yourself, too. Just buy a new hot mirror, disassemble your camera and replace it – at least for Leica. Of course, that’s easier said than done if this isn’t the kind of thing you do for a living. For Blackmagic, it’s a little easier, because it’s not attached to the sensor itself and is easily replaceable by the user.

Still, although the video is to help promote Kolari’s repair service and replacement hot mirrors, the knowledge contained within can help extend the life of your camera. It’s not an issue that everyone’s going to face. But it is something you’ll probably want to keep an eye on if you’re shooting certain brands and models of cameras.

It’s also something you’ll want to look out for and factor into the price when looking for used cameras, too. Killer deals don’t look so killer when you have to cover shipping, a replacement hot mirror and installation.

---