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01-02-2019, 11:26 AM   #1
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Need help identifying specks on Pentax-M 150mm lens

Hey folks,

I just received a Pentax-M 150mm lens from Japan, that is supposed to be "near mint". The built-in lens hood is very loose (sounds like maybe they used felt to dampen the hood movement and it's deteriorated) but more concerning is the optics, which look very good when shining a light through the rear, but when viewed from the front, unlit, and at a slight angle, there appears to be something on the rear of the front element (as far as I can tell). This lens has 5 elements in 5 groups so there shouldn't be any separation (if I understand correctly) but it's not dust and doesn't really look like fungus (to me). Anyone have any ideas? Thanks!

-Jonathan

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01-02-2019, 11:38 AM   #2
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Doesn't look like anything I've ever seen... not saying I've seen everything!

Doesn't look like the mold I've seen before.. looks like small fibers really.

What's especially weird for me is the relatively even distribution of the fibers across the element...

Maybe they are fibers from the felt you say had deteriorated.

Definitely not near mint!
01-02-2019, 11:38 AM - 1 Like   #3
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It could be fibers from a decayed case but it looks like the after effects of Fungus from the looks of it.
01-02-2019, 11:57 AM   #4
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Dried condensation?

01-02-2019, 12:02 PM   #5
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A vote for fungus. Sometimes fungus eats off a layer or two of the coating.
01-02-2019, 12:16 PM   #6
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QuoteOriginally posted by Docrwm Quote
It could be fibers from a decayed case but it looks like the after effects of Fungus from the looks of it.
Exactly the reason that I view with suspicion any lens for sale "with original case". Those things are a breeding ground for potential fungus and if I do end up with one it goes straight in the bin.
01-02-2019, 12:23 PM   #7
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Fungus! Speckled variety.

Easy lens spanner looks like rubber grip needed to remove nameplate job to take out the objective and clean (I use tissue moistened with household mould cleaner) on a simple lens like M 150mm. Unlikely to have affected coatings - can happen but I hardly ever see it.
01-02-2019, 12:36 PM   #8
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QuoteOriginally posted by pentaxus Quote
A vote for fungus. Sometimes fungus eats off a layer or two of the coating.
QuoteOriginally posted by pschlute Quote
Exactly the reason that I view with suspicion any lens for sale "with original case". Those things are a breeding ground for potential fungus and if I do end up with one it goes straight in the bin.
QuoteOriginally posted by marcusBMG Quote
Fungus! Speckled variety.

Easy lens spanner looks like rubber grip needed to remove nameplate job to take out the objective and clean (I use tissue moistened with household mould cleaner) on a simple lens like M 150mm. Unlikely to have affected coatings - can happen but I hardly ever see it.
My thoughts exactly. I have had lenses etched by mold over the years. Depends on a variety of factors like type of mold, age of infection, storage, etc.


I've been pleased with these rubber grips:
amazon.com : Japan hobby tool Vacuum Pad Camera Parts Opener for Camera Lens Repair Made in Japan : Slr Camera Lenses : Camera & Photo?tag=pentaxforums-20&

01-02-2019, 12:40 PM   #9
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Thanks everyone for the info and tips about disassembly. If I decide to try to clean it up, assuming it's only on the rear of the front element, there aren't any re-alignment issues (i.e., I can just place the front element back in place and it's correct?) I really don't want to destroy an otherwise good lens.

-Jonathan

01-02-2019, 01:00 PM   #10
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QuoteOriginally posted by jhankins Quote
Thanks everyone for the info and tips about disassembly. If I decide to try to clean it up, assuming it's only on the rear of the front element, there aren't any re-alignment issues (i.e., I can just place the front element back in place and it's correct?) I really don't want to destroy an otherwise good lens.

-Jonathan
The old M lenses were both simple and robust. If it is only the front element it is usually pretty straightforward a process. I prefer hydrogen peroxide to clean away fungus along with exposure to the gasses from heated copper (pennies usually work fine because Copper, and its alloys brasses, bronzes, cupronickel, copper-nickel-zinc, and others, are natural antimicrobial materials).
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