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05-13-2014, 03:05 AM   #1

Join Date: Mar 2010
Location: Frankfurt am Main
Posts: 1,092
Fungus on SMC-M 4/50 macro

I recently purchased a SMC-M 4/50 macro. It looks quite good and functions well, but there is fungus starting on the back of the front lens, presently only at the borders. It was not expensive, so I decided to give it a try.

Now I have 2 questions.
  1. I have used an old (beginning of the seventies) UV burner device for about 12 minutes as a starter. This should be roughly the same dose of UV-B and UV-C as a full midsummer day in high mountains or at the sea; and I will repeat that. I know that - in theory - this should stop spreading or even finally kill the fungus. But has anyone here ever made a reality check?
  2. I cannot compare, but it seems IQ is not yet influenced - probably contrast at F4, but in this respect the 4/50 macro is not the best anyway (so I heard). But if spreading does not stop, or if I finally am not satisfied with IQ, I may have to clean it. I searched the internet and this forum for any hints about disassambling, but no success. Has anyone done it, or knows a link to a description? I would think - despite of the simpler design - there could be more problems than with some other lenses because of the extremely deep sitting front lens, and the very long throw for distance setting.

Last edited by RKKS08; 05-13-2014 at 06:23 AM. Reason: spelling
05-13-2014, 04:26 AM   #2

Join Date: Mar 2014
Location: Sydney
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Posts: 442
Had a similar situation with a Super Tak 50mm. Searched around and found this on Youtube:

After watching the video closely, went and spent $100 to get it done properly.
05-13-2014, 04:54 AM - 1 Like   #3
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Join Date: Sep 2011
Location: Stockholm
Posts: 197
1) What I've heard is; when you notice fungus in a lens, it's probably already dead. With the UV burn, I'd be pretty certain. That's not to say that more fungus couldn't appear, as the spores are pretty much everywhere, and the conditions where obviously right once.
2) The edges of the front lens aren't likely used much on APS-C cameras. At macro distance, even less of the front lens is likely used. So it may not be necessary or even helpful to disassemble it. If you do, I've not taken apart that particular lens, but most pentax lenses I've seen can be taken apart from the front to get to the front elements. Usually, the name ring can be unscrewed, and you go on from there. For cleaning fungi residue, don't use strong chemicals, as they'll destroy the sensitive inner coatings. I've had success with human saliva. It contains enzymes to take apart proteins and leave most other matter intact.
05-13-2014, 09:03 AM   #4

Join Date: Mar 2010
Location: Frankfurt am Main
Posts: 1,092
Original Poster
Thank's for all advice so far yet.

I asked the first of my 2 questions, because suggestions to kill lens fungi with UV are all over the net, not only in this forum. But to me it seems most (or all?) of these advices are given from hearsay, or citing biological theories.

The second question was because I read douzens of descriptions about how to disassemble various lens types from the front end.
I just wanted to be prepared in case there is something special about doing it with the SMC Pentax-M 4.0/50mm macro.


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