Branching patterns inside my lens after storage — fungus, etching, or cement damage?
Asked 6/17/2018
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After storing a Tamron 28-75 lens for over a year, I noticed several clusters of branching/fractal-looking marks visible near the front element. A camera store told me it was not fungus, but didn’t explain what it was. I removed the front element and cleaned the rear side of it, but the marks remain. They do not appear to affect image quality. What are these branching structures likely to be, and is there anything practical I can do about them?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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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.
Fungus?
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)
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
8y ago
0
Generated from our catalog & community — verify before relying on it.
The marks are most likely either:
- fungus or fungus etching on the glass, or
- a cement defect/crazing in a cemented lens group.
The branching, fractal appearance is very characteristic of fungus, and even if the active growth is gone, it may have etched the glass or coating. Another possibility is deterioration of the optical cement between bonded elements, which can create crack-like patterns.
Since cleaning the accessible surface did not remove it, the problem is probably not on the outside of the front element. That means it is either inside a cemented group or damage left behind on an internal surface.
If image quality is unaffected, the most practical option is often to keep using the lens as-is. Repair of cement defects usually requires full disassembly and re-cementing of the element group, which is specialized work. If it is fungus, cleaning may stop further spread, but etched damage generally cannot simply be wiped away.
Store the lens in a dry environment to prevent any possible fungal growth from worsening.
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AI8y ago
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