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Archive 2011 · Reducing radioactive yellowing?

surf monkey
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p.1 #1 · p.1 #1 · Reducing radioactive yellowing?

I'm not sure how much has been posted on this subject so I'm trying to get more info.
I recently got a Minolta Rokkor 58f1.2 and the images are quite yellow.

With radioactive lenses that exhibit yellowing, how do you eliminate or reduce the yellowing?
I've read that exposure to sunlight reduces it. How long in the sun will make a difference? How much of a difference will it make? Does the yellowing return and do I need to expose to the sun on a regular basis?

Mar 13, 2011 at 12:20 PM

jcolwell
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p.1 #2 · p.1 #2 · Reducing radioactive yellowing?

Here's how it's done for older Pentax glass, http://web.aanet.com.au/bayling/repair.html

Mar 13, 2011 at 12:24 PM

Bob955i
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p.1 #3 · p.1 #3 · Reducing radioactive yellowing?

I had a Zeiss Jena Pancolar 50 that was yellowed and as Scotland (where I live) is not noted for sunlight, what I did was apply Bacofoil with the shiniest side inwards at one end of the lens as a crude reflector and shone a small UV lamp in the other. Whole process took about a month IIRC but it worked, at least for me. That was a couple of years ago now and the yellowing hasn't returned.

Sunlight's OK but you don't want it heating the lens excessively (might melt optical adhesives and cause lubricants to migrate where they shouldn't) and you don't want the lens setting fire to anything either if you know what I mean.

Mar 13, 2011 at 12:30 PM

Steve Spencer
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p.1 #4 · p.1 #4 · Reducing radioactive yellowing?

Set the lens in the sun for a week or two or a day or two with a UV flashlight shining through it and it should get rid of the yellowing. I hope that helps.

Mar 13, 2011 at 01:06 PM

surf monkey
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p.1 #5 · p.1 #5 · Reducing radioactive yellowing?

Bob955i wrote:
Sunlight's OK but you don't want it heating the lens excessively (might melt optical adhesives and cause lubricants to migrate where they shouldn't) and you don't want the lens setting fire to anything either if you know what I mean.

I live in San Diego and the weather has been cool and sunny as of late. Should I just leave it outside in the bright sunlight or should I protect it from the elements under glass? Do I need to have both end caps off? Is there a certain temperature that I should worth about?
For me, buying a UV flashlight seems to be an unnecessary expense since I have a natural resource. Will a typical UV flashlight provide more power (and therefore faster treatment) than the sun?
I was hoping a few days in the sun might be a good start.

Mar 13, 2011 at 02:56 PM

surf monkey
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p.1 #6 · p.1 #6 · Reducing radioactive yellowing?

Steve Spencer wrote:
Set the lens in the sun for a week or two or a day or two with a UV flashlight shining through it and it should get rid of the yellowing. I hope that helps.

Thanks, I guess that answers my previous questions.

Mar 13, 2011 at 02:57 PM

surf monkey
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p.1 #7 · p.1 #7 · Reducing radioactive yellowing?

jcolwell wrote:
Here's how it's done for older Pentax glass, http://web.aanet.com.au/bayling/repair.html

Not the answer I was looking for.

Looks like a great way to spread the radioactive elements into the environment though.

Mar 13, 2011 at 02:59 PM

jcolwell
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p.1 #8 · p.1 #8 · Reducing radioactive yellowing?

True, but I suspect the pieces of sharp glass would be a greater threat than the Thorium residue.

Mar 13, 2011 at 03:04 PM

Bob955i
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p.1 #9 · p.1 #9 · Reducing radioactive yellowing?

surf monkey wrote:
I live in San Diego and the weather has been cool and sunny as of late. Should I just leave it outside in the bright sunlight or should I protect it from the elements under glass? Do I need to have both end caps off? Is there a certain temperature that I should worth about?
For me, buying a UV flashlight seems to be an unnecessary expense since I have a natural resource. Will a typical UV flashlight provide more power (and therefore faster treatment) than the sun?
I was hoping a few days in the sun might be a good...Show more →

You can leave it on your windowsill on the inside as long as it doesn't focus on anything. Take both end caps off and face it towards the sun. As far as temperature's concerned, you don't want the lens to get hot to the touch - slightly warm should be OK. A UV light is safer as there's no heat generated and you can generate UV whenever you need to for as long as you need to. Like I hinted, I live in the UK and long-term sunlight is almost a luxury here so I used a UV lamp purely for consistency and to get the job done.

Mar 13, 2011 at 03:04 PM

surf monkey
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p.1 #10 · p.1 #10 · Reducing radioactive yellowing?

Bob955i wrote:
You can leave it on your windowsill on the inside as long as it doesn't focus on anything. Take both end caps off and face it towards the sun. As far as temperature's concerned, you don't want the lens to get hot to the touch - slightly warm should be OK. A UV light is safer as there's no heat generated and you can generate UV whenever you need to for as long as you need to. Like I hinted, I live in the UK and long-term sunlight is almost a luxury here so I used a UV lamp purely...Show more →

Is there a simple & inexpensive way of setting up a UV lamp or flashlight?

Mar 13, 2011 at 07:48 PM

Ed Sawyer
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p.1 #11 · p.1 #11 · Reducing radioactive yellowing?

uv LED flashlight from Ebay:$10.
aluminum foil from around the house, make a hood/cone, and put the flashlight in one end, lens in the other. : $free
2-3 sets of batteries: $10
a few days time: free

that's about all it takes. periodically rotate the flashlight so the light reaches all parts of the lens. I cleared a few lenses this way.

-Ed

Mar 13, 2011 at 10:38 PM

flashinm
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p.1 #12 · p.1 #12 · Reducing radioactive yellowing?

I bought a blacklight from Wal-Mart for $10. Put foil over the front and place the rear about an inch from the bulb. Yellowing will be completely gone within a week.

Mar 13, 2011 at 10:47 PM

surf monkey
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p.1 #13 · p.1 #13 · Reducing radioactive yellowing?

Awesome guys, thanks for the tips.

Mar 14, 2011 at 12:02 AM

staticInc
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p.1 #14 · p.1 #14 · Reducing radioactive yellowing?

My recommendation:
As long as the weather is cold and sunny, leave it outside on a table where the wind can cool the barrel and no window is in between the lens and the sun. It may be useful resting the lens on a mug pointing directly into the sun. Realign the mug from time to time to keep the sunlight shining directly into the lens.
Window panes may reflect most of the UV-rays since the sunrays are not passing vertically but sometimes in a flat angle, which causes more reflections than direct impact.

This process worked perfectly with my Rokkor 28/2.5. Left it outside for a week whenever the sun was shining. The barrel didn't warm up at all, on the contrary. It got chilled by a slight breeze. No warming, but plenty of UV rays.

Good luck!
sI

Mar 14, 2011 at 06:08 AM


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