I packed a Tamron 28-75 lens away for over a year. When I took it out of storage examined it, I found clusters of branching structures on or in the front element.

I Took it to a camera store and they said it wasn't fungus, but they didn't tell me what it was. I have removed the front element and cleaned the backside but it does not fix the issue.

It does not impact picture quality at all. Not sure what to do.

clusters of branching structures on lens

  • 3
    \$\begingroup\$ If there's another store nearby, I suggest getting a second opinion. \$\endgroup\$
    – Crazy Dino
    Jun 17, 2018 at 20:36
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    \$\begingroup\$ What effect is it having on the picture? \$\endgroup\$
    – Laurence
    Jun 17, 2018 at 23:02
  • \$\begingroup\$ This had been over a year now. I've put the lens away for some time. In fact it is not impacting picture quality at all. It's on a Tamron 28-75. \$\endgroup\$ Jun 17, 2018 at 23:33
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    \$\begingroup\$ Given the even distribution I'd say not fungus. Fungus hyphae have a root like structure and would have density around the edges or point of penetration. Alan Marcus answer sounds like most likely. \$\endgroup\$
    – Lex
    Jun 18, 2018 at 1:18
  • \$\begingroup\$ I recommend taking a look through a microscope. You can get a decent USB microscope for around 30$, and a purely optical and portable for half that. (If nothing else, it is a great excuse to buy a microscope.) \$\endgroup\$
    – Davidmh
    Jun 18, 2018 at 11:49

2 Answers 2


Cement Defects

Camera lenses are constructed using several individual lenses packed into the lens barrel to correct lens aberrations. Some are air-spaced, while others are are cemented together. The cement of choice is a super clear resin made from the sap of the Canadian Balsam Pine tree. In recent years, this glue has been fabricated in a lab.

  • Other Organisms: Glues made from natural sap make good food for beasties. The synthetic glue is somewhat immune.

  • Crazing: Lens cements are also subject to crazing, a network of fine lines that resemble cracks, which is caused by the glue becoming brittle. This can happen when they are exposed to extreme temperatures.

The only way to repair cement defects is to disassemble, dissolve away the glue, and re-glue. Finding someone to do this will be difficult and expensive. The good news is, often these types of defects are mainly cosmetic. They only minimally degrade image quality.


The even distribution makes fungus less likely because fungal hyphae have a root like structure and would have density around the edges or point of penetration. (@Lex)

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    \$\begingroup\$ @ xiota -- Crazing is cause by the glue becoming brittle. Maybe an extreme temperature change did this deed. \$\endgroup\$ Jun 17, 2018 at 23:14

It looks pretty much like fungus to me — the branching is characteristic. It might, however, not be fungus itself, but etching on the glass as a result of fungal growth.

It's true that fungal growth on lenses is generally all connected. That's not necessarily true, though. Fungus can grow from lots of different "starter" spots as well. This blog post shows an example of fungus growing this way, which I've excerpted here:


Of course, it's not as pervasive and there is more of a circular pattern to each "bloom", but this demonstrates that it's not always a big patch growing from the edge.

Meanwhile, I'd expect lens glue crazing to look more like a series of little lines, and not nearly so fractal. But I've never seen that in person either way.

One possible guess — and it's just a guess! — is that it was all connected and this is where it was enough to etch the glass.

  • \$\begingroup\$ If it is fungus can it affect my camera and spread? Should I toss the lens? \$\endgroup\$ Jun 17, 2018 at 18:22
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    \$\begingroup\$ Fungus is everywhere, so there's no special worry about it spreading from one lens to another. But if it is, and especially if it has etched the glass, and further especially if it is a low-cost lens (like a kit lens), it's probably not worth trying to salvage. \$\endgroup\$
    – mattdm
    Jun 17, 2018 at 18:49

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