Black Light to reduce throium yellowing on lens?

[mike_h5]

It's starting to rain often in california now, and it's cloudy more

often than not. So I was thinking about buying a UV light. But I'm

not sure if that would work the same way as the sun. <p> <a

href="http://en.wikipedia.org/wiki/Image:Fluorescent_Black-

Light_spectrum_with_peaks_labelled.gif">Wikipedia shows a wavelength

chart of black light<a> <p> <p>Would these wavelengths neutralize

the yellowing? <p> I bought an SMC Takumar 50mm F/1.4 lens at first

with the yellowing. I put it outside for about two weeks and it

cleared up mostly, but still has a bit of yellowing. I later bought

a Super- Multi-Coated Takmuar 50mm F/1.4 lens when hearing that

these slightly older lenses have no yellowing. But again there is

yellowing. I also have a Super-Multi-Coated Takumar 35mm F/2 that's

yellowed.

[grinder]

What about getting your dentist to use thier high powered uv curing light on the lens for a minute or so? They also have the benifit of being very concentrated so you can reduce the exposure to the plastic parts. It is worth asking about.

[andrew robertson]

That's OK. You'll still get enough UV into the lens even with clouds.

[greg_erker]

I recall that people on the Pentax Discuss mailing list have

de-yellowed their lenses by exposing them to sunlight for

a while (a week or two maybe?). Just make sure the lens can't

focus the sun's image onto something and start a fire.

 

Greg

[mike_h5]

So would the black light work?

I'm thinking about buying a cold cathode UV light. It only costs $6 for two tubes.

[dan_fromm1]

I've cleared three Taylor, Taylor, Hobson process lenses using a 20w coiled BLB fluorescent tube. It took about two months.

[michael_briggs2]

<p>I've greatly reduced the amber color of an Aero-Ektar and an 35 mm f1.4 Nikkor using BLB fluorescent bulbs. It takes a long exposure -- weeks. The screwmount 50 mm Takumar that I have measured with a Geiger count is much radioactive in the back -- the count rate is surprisingly high for the size of the lens -- my guess is the rear most glass element is the one with thorium. I'd try exposing the lens from the back. If you exposed from the front, some of the UV light might be absorbed by the glass or coatings because it reached the thorium glass.</p>

 

<p>Here are some previous threads: <i>Aero-Ektars: Does UV light remove the brown stain?</i> at <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005obo">http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005obo</a>, <i>Yellowed Takumar a Good Thing?</i> at <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00D80Y">http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00D80Y</a> and <i>yellowish cast looking through 35mm f1.4 [Nikkor]</i>

at <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0054IM">http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0054IM</a>.

</p>