Thorium in my lens? nope.
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.
I have 3 thorium lenses by different manufacturers, but I don't have any concerns about them affecting my health. I believe the main reasons thorium stopped being used were 1, improvements in technology allowed other materials to be used in it's place, and 2, concern over worker's safety. It's true that thorium lenses put out too little radiation to do any harm, but the large amounts used in the manufacturing of the glass likely posed a greater health risk.
I have the Canon FD 35mm f2 Thorium lens, and it's such a great lens I'll take the risk, and wear lead lined boxer shorts.
If you smoke, drive a car, climb a ladder, or fire up a barbecue grill, focus on reducing those very real risks, rather than the risk of thorium-emitted alpha particles.
If the OP was at all seriously concerned (hard to read people onlne), then this was yet another example of the common human fixation on remote, even minuscule, risks while ignoring the real ones whose abatement, however, would require habit change or other inconvenience.
And this tendency would be merely an amusing quirk were it not for its implications for public policy. And yes, widespread irrational public fear, leveraged by the lunatic part of the enviro movement, HAS likely prevented more widespread adoption of nuclear power generation in the US.
(Hadn't planned on mounting the soapbox quite so early this morning!). ;-)
Well, in terms of the uncontrolled disastrous human population growth, I would suggest going without
Originally Posted by benjiboy
"The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true.
" - William M. Ivins Jr.
"I don't know, maybe we should disinvent color, and we could just shoot Black & White.
" - David Burnett in 1978
"Analog is chemistry + physics, digital is physics + math, which ones did you like most?
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No fear, got to protect the family jewels.
Originally Posted by Marco B
I thank you for the test results. Any data in regard to radioactive lenses is always helpful. Though some have dismissed the detrimental effects of thorium in lenses, others have found problematic levels of radiation. Here is an interesting link: http://forum.mflenses.com/best-of-ma...-4-t11295.html
With regard to the subject of overpopulation, the common contemporary hypothesis is gravely erroneous. The world is simply not becoming overpopulated. Europe is shinking at an alarming rate, and, if the current trend continues there, Europe will not repopulate itself (as the continent is currently well below its repopulation rate). The entire population of the earth could fit into the land area of the US, with plenty of room. Likewise, the entire population of the US could fit into the state of Texas, again with ample space. Here is an interesting discussion: http://economics.gmu.edu/wew/article...on-Control.htm
Last edited by FilmOnly; 11-23-2009 at 09:41 AM. Click to view previous post history.
Here's an interesting item - the first hit on a google search for "thorium lenses."
As a Nuclear Engineer I would not put too much confidence in your measurements unless you had a radioactive source to verify calibration/function of a GM device from the 1960's.
In any event unless you grind up a lens containing a radioactive element and injest, there will be no harm from external exposure and since the glass will quickly pass through your digestive system, no quantifyable internal effects anyway.-Dick
I would be interested to know how the 50/1.4 S tests on correctly functioning equipment. The brownish tint of the lens gives me pause.