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Question about yellow glass on old lenses
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PostPosted: Tue Aug 17, 2010 11:35 am    Post subject: Question about yellow glass on old lenses Reply with quote
Is it true that you just can put the lens in the window against the sun for some days to make the yellowing bleach? Surprised


PostPosted: Tue Aug 17, 2010 11:54 am    Post subject: Reply with quote
this has been discussed several times in length here, search for it.
And yes, it is possible in principle.


PostPosted: Tue Aug 17, 2010 12:22 pm    Post subject: Reply with quote
It is also true that putting optics in the window can focus the sun and start fires. So be careful. Wink


PostPosted: Tue Aug 17, 2010 12:29 pm    Post subject: Reply with quote
Doesn't it also depend on whether the yellow is from decayed glue between elements or from some radioactive effect?


PostPosted: Tue Aug 17, 2010 1:58 pm    Post subject: Reply with quote
PaulC wrote:
Doesn't it also depend on whether the yellow is from decayed glue between elements or from some radioactive effect?


IMO, put it under sun can clean the yellowish from radioactive only. The best is put it directly under the sun light without any glass in front of the lens, because the UV light in the sun light is the key to cure the glass.


PostPosted: Tue Aug 17, 2010 2:23 pm    Post subject: Reply with quote
Success has been reported using Sunlight. Others have used inexpensive long-wave UV lamps. The shortwave UV lamps are more expensive; shortwave UV lamps require safety precautions to avoid eyesight damage!!!

For example 1.4/50 Takumars. The element that yellows is in rear group; point that end toward Sun; again, careful sunlight doesn't get focused starting a fire; some people put aluminum foil over front to reflect light back into lens.


PostPosted: Tue Aug 17, 2010 4:01 pm    Post subject: Reply with quote
uv lamps are not that expensive, and you can de-yellow lens much faster than leaving it on the sun. You can really overheat lens on sun, not good for lubricants (just my opinion, dont rely on that one)

I have deyellowed my takumar overnight with uv lamp (I had it before for UV glueing)


PostPosted: Tue Aug 17, 2010 6:36 pm    Post subject: Reply with quote
http://web.aanet.com.au/bayling/repair.html

aarrgghhhh........ Rolling Eyes


PostPosted: Tue Aug 17, 2010 7:41 pm    Post subject: Reply with quote
Quoting Wikipedia:

Quote:
Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while Silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.


So it sounds like only a small amount of UVA (and barely any UVB and maybe no UVC) would reach your lens by the window, depending on the glass in your window. Then you have people who say that lenses are designed to be very resistant to UV light.

Wouldn't it be easier to make one front lens cap from silica/quartz glass and just store the lens like normal if you're in no hurry?

N.B. I never got on with science so all of the above may just sound like absolute twaddle.


PostPosted: Wed Aug 18, 2010 8:54 pm    Post subject: Reply with quote
egidio wrote:
uv lamps are not that expensive, and you can de-yellow lens much faster than leaving it on the sun. You can really overheat lens on sun, not good for lubricants (just my opinion, dont rely on that one)

I have deyellowed my takumar overnight with uv lamp (I had it before for UV glueing)

+1
I did with my Sonnar 180/2.8 P6, It was perfect.
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