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06-23-2021, 10:49 PM   #1
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Leave lenses in the sun or using UV light bulb?

I am sunbathing my old lenses and wondering if I should do it? Anyone doing it?
I just read a post where OP got a used lens and found nasty things inside. Many people said they are fungus which worry me about my own older lenses. 2 of them haven't been used for a while. None of them show sign of fungus but I am a kind of worry so I sunbath them today and thinking of doing the same to the entire collection.
The old lenses and the limited are mostly made of metal and glass, but some DA lenses has rubber / plastic parts, some have electronic parts inside. I worry the heat might not be good for them. Am I right on that?

Another thing, weather here in Japan getting more and more humid. It is not very bad as for now but it is starting. Let me know if I shouldn’t do it during hot and humid time of the year.

I also have a UV light bulb by the way. I just think that UV from the Sun is a lot stronger than my small UV lamp. If you think UV lamp is better, let me know how long is appropriated.

Thank you in advance.




Last edited by tokyoscape; 06-24-2021 at 12:53 AM.
06-23-2021, 11:07 PM   #2
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While sunlight or UV lamp will kill any live fungus in the lens, you will still need to remove the elements to clean off the dead fungus. UV is used to remove the yellowing caused by radio-active elements in some of the old Takumars,

The danger of putting lenses like these in direct sunlight is the heat can cause the grease inside to run. If you get grease on the aperture blades they will need to come out for cleaning.
06-24-2021, 12:36 AM   #3
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Personally I would not advise sun light, maybe UV is more controlled since it has a fraction of the specter of sunlight, but I wouldn't do that either. The best way is to disassemble the thing and try and remove most of the fungus manually. You will need to do it either way, even if you kill the fungus with light.
06-24-2021, 12:54 AM   #4
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In the right (for the fungus) conditions fungus will grow anywhere. Spores are all around us all the time. Just store your lenses in light, airy, low humidity conditions. You can buy humidity controlled cabinets, or reduce it with moisture absorbing chemicals.

It is unlikely, verging on impossible, for a lens with fungus in it to infect others mainly because the original infection will die off before it can produce fruiting bodies. What you see in lenses is the evidence of a past infection.

06-24-2021, 01:52 AM   #5
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If you are not seeing it now I would not worry too much, but I believe the light would be much better than the sun. I have a dehumidifier cabinet to store lenses in just as a safety precaution since I live in a very humid area, even though if your house is air conditioned that is probably enough.
06-24-2021, 06:15 AM   #6
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I used sunlight, with the lens wrapped in foil (bar the front element of course) to prevent it getting too hot. That worked well here in sunny Spain but I don't think it was summer so it wouldn't have been really intense sunlight.

Classic lenses shouldn't suffer much from a bit of heat, newer ones would.
06-24-2021, 06:48 AM   #7
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I'd use UV if you have a yellowing of the lens elements caused by aging, but if you don't have any noticeable fungus growth, I would just store the lenses in a polyethylene bag with a desiccant to make sure the lens is well dried out (take them out for use and return them when done). Too much UV light can be detrimental to lenses if not needed so why the risk? As others have mentioned, leaving them in the sun is a non-starter. You don't want to "cook" you lenses for all kinds of reasons.

06-24-2021, 08:07 AM   #8
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QuoteOriginally posted by tokyoscape Quote
Leave lenses in the sun or using UV light bulb?
Unless you are attempting to clear yellowing from thoriated elements, there is no benefit to exposing your lenses to the sun or UV light. Humidity and temperature control are key for lens storage in regions where condensing humidity is a common environment.


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06-24-2021, 08:11 AM   #9
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QuoteOriginally posted by Jonathan Mac Quote
Classic lenses shouldn't suffer much from a bit of heat, newer ones would.
Heat causes migration of lubricants out of where they are supposed to be and into where they are not supposed to be. If a lens' focus action is uneven, heat was probably the cause. Oil-fouled aperture blades didn't start that way...blame heat.


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06-24-2021, 11:18 AM   #10
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As far as power level of the UV light at earth's surface from the sun the total irradiation from the sun over a square meter is about 1000w at earth's surface and that is for all light with the UV portion being a small portion. I paid about about $20 for a 10w UV lamp and it is pretty small so I bet if I were to cover 1 square meter with lamps like it I would probably be near 1000w total but instead of it being a big mix of light it would just be UV. I used this lamp to clear my old radioactive takumars of yellowing and keep them that way. I have used it once to disinfect my lenses as a preventative measure to ensure that fungus doesn't become a problem but probably won't do it again for several years.
06-24-2021, 11:10 PM   #11
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I try to expose my lenses to light daily, mostly by burning through film .. (sorry, couldn’t resist)
06-25-2021, 02:28 PM   #12
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Thank you all for the answers. It's good to know so that I don't try something useless and possible damage my lenses again.
09-14-2021, 12:37 PM   #13
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As most lenses today contain plastics, I would avoid exposing them for long duration to the heat of burning sun.
Degrading / aging or deformation is a risk if you ask me.
09-14-2021, 01:13 PM   #14
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Sunbathing your lenses as a preventative measure I'd say is inappropriate. Fungus will not start in an airy humidity controlled home. If your place gets humid you'd want to get a cabinet that controls for that.
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