Killing miniscule lens fungus w focused sunlight?

[Andre Noble]

I have a phenomenally sharp, prized modern make LF lens that I recently noticed has three isolated, very miniscule growths of fungus right next to each other on an internal element in the rear cell. Otherwise the lens is clean throughout. I talk to Adam at SK Grimes and know this conventional route of dissasembling the lens for cleaning is a possibillity. I am concerened about losing some performance on the lens after re-assembly. Any feedback on this?

I am also considering another method which would not involve dissasembly, that is killing the fungus in vitro by using focused sunlight onto the fungus for a short time. Any feedback you can offer on this?

Thanks in advance.

[paulr]

"I am concerened about losing some performance on the lens after re-assembly"

yes ... you'll never get the elements centered and aligned properly.

i don't know about killing fungus by irradiating it ... but it won't make the existing fungus go away. i think taking it to a technician, preferably a tech rep of the company that made it, is the best bet.

[George Stewart]

I'd recommend 4-5 hours in the sun before shipping it anywhere. A focused beam of light might cause the fungus to cook (perhaps making matters worse). In other words, perhaps the slow method is better than brining in the nukes and leaving a black-carbon mess in your lens.

[Dan Fromm]

Paulr, if he's talking about undoing the retaining rings, removing the glasses, and then reassembling, where's the problem? Are you thinking of problems after uncementing and recementing?

[GPS]

Focused sunlight will not kill the fungus - the glass will spread the heat before it gets on the fungus itself. If you prolong the exposure the heat could break the lens.

[E. von Hoegh]

Mr Sophmore, If your lens is serviced by a competent technician, centering and alignment will not be an issue. If the fungus goes untreated the lens will eventually be useless.

[Conrad Hoffman]

Fungus- time is of the essence. You can't kill it with heat, because the lens would be damaged first. You can't kill it with UV because the lens doesn't transmit enough of the right wavelengths to get the job done. If you leave it there, it will destroy the coating and etch the surface of the glass. Left long enough, it will even eat deep pits in the surface of the glass. You must get this serviced now!

Centering- this is one of the most misunderstood topics around. Modern lenses are centered when the edges of the elements are ground, and the results of modern equipment are nearly perfect. After that, it's just a matter of tolerances on the machined sections that hold the elements. Almost no lenses have provision to adjust centering in any way, nor is it necessary. In theory one could rotate elements and attempt to get the retaining rings tightened with the elements in specific positions, but actually doing it would be difficult at best. Lenses get dropped into their receptacles and that's that. BTW, it appears SK Grimes has excellent equipment for checking centering. Cementing is usually done with mechanical fixtures, and good technicians will get it right. Your lens doesn't sound like it needs to be uncemented anyway. Bottom line, don't worry about centering or loss of performance. It's a non-issue. Loss of performance due to fungus, however, is a real issue.

[Rob_6274]

My Minolta 7s has tiny fungus infestation (looks like spider web) when I got it. I exposed it to sunlight for an hour, keeps using it (BTW, it's sharp lens) and stores it in dry environment with my other lenses. Look like it stops growing, it does not grow bigger. If I were you, I would not worry and keep using the lens and store it in really dry container with active dessicant. That big foodsaver vacuum container + dessicant is a nice dry container. A very small infestation won't affect the optical performance, especially when you shoot at small aperture.

[GPS]

While keeping a lens in very dry environment can eventually kill the fungus in a long time exposing the lens for 1 hour to the sun does no difference at all. To see with your eyes the difference between a growing fungus and a dead one is what I would call the ultimate exercise in patience and futility. The fungus keeps its own humidity in itself (if not it would be killed with whatever period of drought). The fungus spores can survive a very long period of drought too only to become a live fungus whenever the humidity allows it again.

[Jerry Flynn]

SK Grimes disassembled and recemented a lens for me (a '70s vintage 180mm Symmar) and I have had no performance issues with the lens.