Lens fungus: is this even possible?

[Ten301]

I bought an almost pristine Praktica MTL 5 about a year ago on the auction site. I say "almost" because, even though the body was like new, the Pentacon 50mm 1.8 lens had what I would describe as a moderate amount of fungus. I read that exposing a lens to sunlight for a period of time sometimes helps, so I figured maybe a UV blacklight might do the same. I had one I use for Halloween decorating, so I placed the lens about 1" from the fluorescent tube so the UV light would shine through the lens and kept it there for three days. At the end of the three days the fungus looked unchanged, so I threw the lens in a box and didn't think much of it. No big deal.

Tonight I happened to be looking through the box and came across the lens. It's now crystal clear with no trace of fungus. No residue, nothing. I would think that even if the blacklight killed the fungus it would still leave marks or etching on the glass, but nothing is there. I'm a bit perplexed. Anyone else have a similar experience?

 

[RalphLambrecht]

I bought an almost pristine Praktica MTL 5 about a year ago on the auction site. I say "almost" because, even though the body was like new, the Pentacon 50mm 1.8 lens had what I would describe as a moderate amount of fungus. I read that exposing a lens to sunlight for a period of time sometimes helps, so I figured maybe a UV blacklight might do the same. I had one I use for Halloween decorating, so I placed the lens about 1" from the fluorescent tube so the UV light would shine through the lens and kept it there for three days. At the end of the three days the fungus looked unchanged, so I threw the lens in a box and didn't think much of it. No big deal.

Tonight I happened to be looking through the box and came across the lens. It's now crystal clear with no trace of fungus. No residue, nothing. I would think that even if the blacklight killed the fungus it would still leave marks or etching on the glass, but nothing is there. I'm a bit perplexed. Anyone else have a similar experience?

no experience but, something crawled into your box and munched ate the fungus or did you keep antibiotics in the box?

 

[shutterfinger]

Yes, uv light kills fungus. Fungus does not always etch glass. Its likely the mold in the lens died and turned to dust which is still inside the lens. Shake it then look through the lens again, there may be spots inside the lens afterwards.
Best to disassemble it and clean the elements and barrel.