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Can a UV lamp kill fungus and make the lens safe for use?
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PostPosted: Fri Nov 14, 2014 4:36 pm    Post subject: Reply with quote

Your calculation does sound good.
But transmission for 254nm is very low for most optical glass.
Take for example BK7 glass, for example for 10mm thickness - no data for 250..260nm:
310nm: 57.4%
300nm: 29.2%
290nm: 6.3%
No further measurments given - even with wavelength values down to 250nm in the datasheet. Other glass even has last data at 350nm. It seems they give values as long as their transmission is 0.1% or higher.

Aside from the glass itself the antireflection coating is also not optimized for 254nm UV transmission. So there will be another low percentage factor.

For lenses with fungus I try to clean the fungus, and afterwards give it some sun UV bathing - fungused surface directly facing the sun. Likely with no big effect - but also with no cost or high effort.
But as main factor I also see correct humidity for storage.


PostPosted: Mon Nov 17, 2014 4:02 pm    Post subject: Reply with quote

Right, my UV treatment space is set up, I think this should be safe enough for my eyes (for obvious reasons, the pictures show a normal lamp instead of the UV-C lamp):









I'll put some aluminium foil under the lenses to reflect some UV back up the lens, all other surfaces are either wood or cardboard.
AFAIK, wood and paper/cardboard should mostly absorb UV rather then reflect it.

The lens next to the 85/1.8 is a Minolta MC 28mm f/2.5 with a slight yellow tint (due to radioactive glas elements), UV-treatment is supposed to help with that...

EDIT:
Here's the setup in action:



Obviously, I took the photo without looking.

Note:
My setup should deliver at least 130W/m² of UV-C to the lenses' front elements.
At sea level, daylight (at the equator, around noon) contains ~80W/m² of UV-A, ~4W/m² and <1W/m² of UV-C.


PostPosted: Mon Nov 17, 2014 7:14 pm    Post subject: Reply with quote

Nice looking setup. Does the lamp get hot when used? If so, have you thought of ventilation inside the cabinet to avoid melting the grease inside the lens(es)?


PostPosted: Mon Nov 17, 2014 8:18 pm    Post subject: Reply with quote

sceptic wrote:
Nice looking setup. Does the lamp get hot when used? If so, have you thought of ventilation inside the cabinet to avoid melting the grease inside the lens(es)?


The lenses feel slightly warm after a couple of hours, that's it, It's just an 11W CCFL after all.
I'll put a thermometer next to the lenses but I doubt it'll ever measure anything but room temperature...


PostPosted: Mon Nov 17, 2014 9:33 pm    Post subject: Reply with quote

sceptic wrote:


Also, consider that most glass absorbs UV light, so it may actually never reach the fungus inside the lens.



Bingo!! You nailed it. That's the controlling paradigm. Dunno whether UV will kill fungus or not. It might. But UV cannot kill fungus if it is unable to REACH the fungus!!

Except for fungus on the front of the front element, or on the rear of the rear element, of any lens, the first step to try a UV light kill is:

1. Disassemble the lens Wink


PostPosted: Mon Nov 17, 2014 10:02 pm    Post subject: Reply with quote

guardian wrote:
sceptic wrote:


Also, consider that most glass absorbs UV light, so it may actually never reach the fungus inside the lens.



Bingo!! You nailed it. That's the controlling paradigm. Dunno whether UV will kill fungus or not. It might. But UV cannot kill fungus if it is unable to REACH the fungus!!


Well, UV-treatment seems to clear yellowing induced by radioactive lens elements... UV-absorption can't be 100%.
In typical glass, absorption rates are lower for UV-A and that's what normal UV lamps emit (used as blacklights and in bug zappers, peak around 365nm). I'd guess that most most people who have tried UV light on their lenses have used normal blacklights.
If UV-A is what kills the fungus, I would need a stronger UV-A (~365nm) lamp.

On the other hand, most UV sources (including the sun, after it's past the atmosphere anyway) emit very little UV-C. UV-C is also the most lethal kind of UV for micro-organisms. If UV-C is what kills the fungus, my setup should be far more effective than a normal UV source or sunlight.


EDIT:
I've changed the setup a bit



PostPosted: Wed Nov 19, 2014 1:18 am    Post subject: Reply with quote

It's been running for two days and there are no temperature problems, the thermometer that I've placed right next to the lenses hasn't moved beyond the 20°C mark (the room temp. is ~16-19°C) and the lenses still only barely feel warm to the touch (below 30°C, I think).





There is no smell of ozone, the lamp's 185nm filter seems to be working. So if this turns out to work, ozone procuction inside the lens is probably out as a cause. (And if it doesn't work at all, UV-C is out out too and high intensity UV-A remains as the only non-invasive option to try)

BTW, it's interesting to see the difference between the blueish light reflected off the aluminium foil (alu is highly reflective across the UV spectrum) and the greenish light reflected of the wood and cardboard (high absorption in the UV spectrum, apparently also at the visible edge).


PostPosted: Thu Nov 20, 2014 9:37 pm    Post subject: Reply with quote

This is interesting - it's an article on lens fungus from a guy that does a lot with microscopes and photography - the web site is a mine of useful information if you're into micro photography.

The article on fungus shows a horribly fungused lens from a machine that projected halogen light, high in UV.

http://www.truetex.com/lens_fungus.htm

And the rest of the site is here

http://www.truetex.com/micad.htm


.


PostPosted: Fri Nov 21, 2014 12:15 pm    Post subject: Reply with quote

First status update:
There's no visible change in the fungus, idk if it's dead or alive but it's definitely not disintegrating.

My two yellowed lenses (Minolta MC 28/3.5, Soligor 17/4) have improved a lot, the tint is almost gone in both.
I've had the Soligor under a UV-A lamp (25W, peak output around 365nm) before without any change. UV-C seems to work a lot better.


PostPosted: Fri Nov 21, 2014 1:57 pm    Post subject: Reply with quote

Perhaps it kills fungus but does not disintegrate the remains?

I remember when I worked as maintenance guy for the clean water supply division for a while ( I usually worked sewage treatment ) we had a lot of boreholes where the disinfection was done with UV lamps, the water was passed over the lamp and became fit to drink. But it did not remove any discolouration in the water or remove particles by breaking them down. We had to filter to remove that.
Some boreholes in very agricultural areas did have high levels of organic impurities, and UV was favoured over chlorination - it killed everything.


PostPosted: Fri Nov 21, 2014 6:11 pm    Post subject: Reply with quote

Boris,
I know you are reluctant to open up the lenses, but that's the only way to clear up the glass. UV light might be killing the fungus, but it won't remove it.
Come over to the tinkering side. It's not as painful as you think. You already have the determination and drive as shown by your lamp research and setup. Now go get some Japanese standard screwdrivers (#00, #000), tubes to unscrew nameplates, and some chemicals (glass cleaner (ammonia/water), alcohol, lighter fluid), and then you will be disassembling/cleaning all your lenses. Lots of satisfaction by taking apart a fungused lens, leaning off the fungus resulting in clear glass, then putting it all back together. Do it. It's fun!!!
(And you may get some great bargains by searching out fungused lenses and then restoring them.

John


PostPosted: Fri Nov 21, 2014 6:18 pm    Post subject: Reply with quote

Exaggerating with UV isn't too good either. All plastic and rubber parts suffer plus general depigmentation. Nevertheless i do support using the lamp to stop fungus growing so lens waits for my repair in better mood.
When fungus cleaned i use UV lamp again to kill germs i let inside the lens when cleaning it.


PostPosted: Fri Nov 21, 2014 6:55 pm    Post subject: Reply with quote

Lloydy wrote:
This is interesting - it's an article on lens fungus from a guy that does a lot with microscopes and photography - the web site is a mine of useful information if you're into micro photography.

The article on fungus shows a horribly fungused lens from a machine that projected halogen light, high in UV.

http://www.truetex.com/lens_fungus.htm

And the rest of the site is here

http://www.truetex.com/micad.htm


.


Good find lloydy. I now know what pericentric and entocentric mean, in relation to my neophyte digiscoping tinkerings...


PostPosted: Sat Nov 22, 2014 8:44 pm    Post subject: Reply with quote

jaecarlos714 wrote:
Boris,
I know you are reluctant to open up the lenses, but that's the only way to clear up the glass. UV light might be killing the fungus, but it won't remove it.
Come over to the tinkering side. It's not as painful as you think. You already have the determination and drive as shown by your lamp research and setup. Now go get some Japanese standard screwdrivers (#00, #000), tubes to unscrew nameplates, and some chemicals (glass cleaner (ammonia/water), alcohol, lighter fluid), and then you will be disassembling/cleaning all your lenses. Lots of satisfaction by taking apart a fungused lens, leaning off the fungus resulting in clear glass, then putting it all back together. Do it. It's fun!!!
(And you may get some great bargains by searching out fungused lenses and then restoring them.

John


I'm planning on doing that (probably mid December), until then I'll just keep the UV setup running.

Pancolart wrote:
Exaggerating with UV isn't too good either. All plastic and rubber parts suffer plus general depigmentation. Nevertheless i do support using the lamp to stop fungus growing so lens waits for my repair in better mood.
When fungus cleaned i use UV lamp again to kill germs i let inside the lens when cleaning it.

Yeah, I noticed that the UV has started to bleach out the black finish on the Minolta... that shouldn't happen anymore:



(BTW, that's not a colour cast, the wood is actually turning green...)