Thorium in my lens? nope.

Lamar · Apr 12, 2013

Just FYI, If you were using a Geiger-Mueller tube it is not going to detect alpha. You need an instrument specifically designed for alpha detection to detect alpha particles. However, with your "Geiger Counter" you may be able to detect the accompanying gamma or any beta radiation, if the detector has a beta window, that maybe emitted by radioactive daughters in the the decay chain.

One_DaveT said:
Tonight I just learned about the use of thorium in lenses up until 1980's. This prompted me to go dig out my 60's vintage civilian defense geiger counter, which I bought years ago after some goof ball medical technician made a wise crack about the half life of the liter of barium I had just quaffed for a cat scan. (fwiw, the drinkable stuff is from a non-radioactive isotope).

Anway, I put my old lenses to the test. I can say after scanning for alpha and beta particle that I believe the following lenses are Thorium-free:

Nikkor-N 24/2.8 pre-AI
Nikor-S.C 50/1.4 pre-AI
Nikkor-P 105/2.5 pre-AI
Nikkor-Q C 200/4 pre-AI

FWIW, I checked a few other lenses:
Zuiko OM 50/1.4
Minolta Rokkor 200/3.5
Minolta Rokkor 50/1.7

After reading that Thorium in lenses goes back to 1937, I checked my Exakta lenses: Steinheil 135/3.5, Westenar 50/2.5..... nope.

In hindsite, after reading wikipedia, it doesn't seem like much of an issue anyway. It says alpha particles from thorium can't even penetrate human skin, so even if I did have a thorium lens, it likely wouldn't be a concern unless I breathed the pulverized dust of a broken lens. Given that the use of it in commercial lenses stopped around 1980 makes me wonder if three-mile island incident in 1979, might have made marketing thorium lenses impossible, and lead to the end of it's use.

Interesting diversion for the evening though.

benjiboy · Apr 13, 2013

A little knowledge is a dangerous thing.

Lamar · Apr 14, 2013

Yes it is. This whole thread is a good example. I've been working in naval and commercial nuclear power since 1985 and about 20 of those years were spent in the field of Health Physics, I see this happen routinely. People learn a little then make statements based false assumptions about a subject to which the general public is very sensitive..... The media is terrible in their understanding of the field and is responsible in a large part for the proliferation of misinformation.

BTW,
I bought on of those JANSJO lights you mentioned in another thread yesterday at IKEA, My 35mm f/1.4 Nikkor-N is under it now. I hope it clears it up, fingers crossed. Thanks for the info.

benjiboy said:
A little knowledge is a dangerous thing.

benjiboy · Apr 14, 2013

Lamar said:
Yes it is. This whole thread is a good example. I've been working in naval and commercial nuclear power since 1985 and about 20 of those years were spent in the field of Health Physics, I see this happen routinely. People learn a little then make statements based false assumptions about a subject to which the general public is very sensitive..... The media is terrible in their understanding of the field and is responsible in a large part for the proliferation of misinformation.

BTW,
I bought on of those JANSJO lights you mentioned in another thread yesterday at IKEA, My 35mm f/1.4 Nikkor-N is under it now. I hope it clears it up, fingers crossed. Thanks for the info.[/QUOTE

My eldest son is also as nuclear phycisist Lamar who works at a leading U.K nuclar reserch facility, he tells me that the radiation dosage emmited by these Thorium lenses are a fraction of the dosage allowed by law to workers in the nuclar industry and are safe as long as you don't sleep for several years with them under your'e pillow

P.S The Jansjo lamp worked brilliantly for me, please let me know how it worked for you.

Lamar · Apr 14, 2013

I just pulled the 35mm f/1.4 Nikkor-N lens after 12 hours under the JANSJO light. I really don't see much change in yellow tint and the light loss is still about a half stop compared to my 35mm f/2.8 ais which is where it was at when I put the lens under the light. I did get a pretty noticeable change a couple of days ago using my wife's salon UV light. 12 hours under it and I got about a half stop improvement and less yellow tint. I think I'll just run the lens under the salon light for another 12-24 hours. No loss on the LED lamp though at only $9. It already has a home here on my desk.

benjiboy said:
My eldest son is also as nuclear phycisist Lamar who works at a leading U.K nuclar reserch facility, he tells me that the radiation dosage emmited by these Thorium lenses are a fraction of the dosage allowed by law to workers in the nuclar industry and are safe as long as you don't sleep for several years with them under your'e pillow

P.S The Jansjo lamp worked brilliantly for me, please let me know how it worked for you.

benjiboy · Apr 16, 2013

Lamar said:
I just pulled the 35mm f/1.4 Nikkor-N lens after 12 hours under the JANSJO light. I really don't see much change in yellow tint and the light loss is still about a half stop compared to my 35mm f/2.8 ais which is where it was at when I put the lens under the light. I did get a pretty noticeable change a couple of days ago using my wife's salon UV light. 12 hours under it and I got about a half stop improvement and less yellow tint. I think I'll just run the lens under the salon light for another 12-24 hours. No loss on the LED lamp though at only $9. It already has a home here on my desk.

It takes more than 12 hours with the Jansjo lamp Lamar, I did mine for about 48 hours, and it helps to place the lens on a small mirror to reflect some of the light back the light back also.

Lamar · Apr 16, 2013

Ok, Thanks. I will try more time. For what it's worth the second 12 hour session in the Salon UV light yesterday didn't make much of an improvement either. I'm still around a half stop slow about the same tint. Probably a logarithmic function, taking more time for the same tint reduction toward the end for a given UV flux...... Just guessing.....

benjiboy said:
It takes more than 12 hours with the Jansjo lamp Lamar, I did mine for about 48 hours, and it helps to place the lens on a small mirror to reflect some of the light back the light back also.

benjiboy · Apr 17, 2013

Lamar said:
Ok, Thanks. I will try more time. For what it's worth the second 12 hour session in the Salon UV light yesterday didn't make much of an improvement either. I'm still around a half stop slow about the same tint. Probably a logarithmic function, taking more time for the same tint reduction toward the end for a given UV flux...... Just guessing.....

P.S It's important to to put the end iof the lamp almost touching the glass of the rear element of the lens.

Lamar · Apr 20, 2013

48 hours later.......... maybe the lens is just a tad better but not enough to say for sure. I'm still at about a half stop slower than my 35mm f/2.8 ais at f/4 with just a hint of yellow still visible, maybe that is just normal for the lens. There was a marked improvement during the first UV session and perhaps and I am just ocd'ing it now. I did check light transmission at f/4 on my 50mm f/1.4 Nikkor-S against my 50mm f/1.8 ais as a cross check. Interestingly the older Nikkor-S was a half stop brighter at f/4..... Things that make you go "Hmmmm". I was using My F4s on spot metering to do the checks. I shot a roll of Ektar using the lens. It produces great pictures. Here is a link to the shots for those that are interested. All shots were with the 35mm f/1.4 Nikkor-N Auto AI on a Nikon F Photomic FTn.

http://www.lamarlamb.com/On-Film/Film-Blog/35mm-f14-Nikkor-N-Auto-Ektar/28969886_ncRTf5

benjiboy said:
P.S It's important to to put the end iof the lamp almost touching the glass of the rear element of the lens.

Thorium in my lens? nope.

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