Super Takumar radioactivity

[Humboldt]

Hello!!
I have been offered a Super Takumar 55/1.8 from a estate distribution. However, I have read these and other older lenses contains thorium and therefore are radioactive. On the internet some people have measured and confirmed it´s radioactivity. My question is: is this a real threat to the health, or is it nothing to care about. As I understand it these Super Tukamars have some nice characteristics, so I would like to try it, but not if they should be avoided due to the radioactivity. Anybody who really knows something about this?

[Frank Fremerey]

Thorium 232 has a very low activity and the Thorium amount in these lenses is very small, the only thing I remember affecting use is the lenses get a color cast with time, yellowish IIRC

[Bjørn Rørslett]

As long as you don't eat them, the lenses are not dangerous.

Joke aside, the radiation levels albeit detectable are low and you only handle the lens for a comparatively short time. Thus total exposure to any radiation is small.

The main issue might be the brownish staining of the glass. Do place the lens facing the sun for a few days to see whether some good dose of UV might mitigate the staining.

By the way, the brand name is 'Takumar'.

[Humboldt]

By the way, the brand name is 'Takumar'.

Yes, I noticed and changed the text above. :-)
Thank you for the answer. It is a bit brownish, or maybe yellowish. I will try the UV treatment, otherwise if it do not help I will use it for black and white.  By the way, an UV filter for protection is not a good idea with these lenses then i Guess.

[JJChan]

H
I've resurrected a couple of excellent SMC M42 Takumars using this:

http://www.ikea.com/us/en/catalog/products/20169658/

Read it here:

http://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/291674-ikea-lamp-takumar-lens.html

I once left a lens in the sun to try to deyellow it and destroyed it by overheating it in the Australian sun (wrecked the very fine lubrication). The lamp is cool and no chance of wrecking your lens.

Good luck

JJ

[Humboldt]

H
I've resurrected a couple of excellent SMC M42 Takumars using this:

http://www.ikea.com/us/en/catalog/products/20169658/

Read it here:

http://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/291674-ikea-lamp-takumar-lens.html

I once left a lens in the sun to try to deyellow it and destroyed it by overheating it in the Australian sun (wrecked the very fine lubrication). The lamp is cool and no chance of wrecking your lens.


Good luck

JJ

Thank you for the tips. It is wonderful. I already own that lamp . I use it for my turntable ;-)

[Bjørn Rørslett]

On a tangent note, those IKEA names are so sweet ... "Jansjö" indeed. Projects the notion of the landscape of Småland from which the IKEA founder originate.

My issue with leaving lenses for UV treatment in the sun is not paying enough attention to the weather forecast and the potential for rain.

[Akira]

Years ago, a Japanese photography magazine put out a special article on the lenses using thorium glasses.  They measured the radiation at Japan Atomic Energy Agency　Nuclear Science Research Institute.

The result was that the amount of radiation was roughly equal to that of natural radiation when you were a couple of meters away from the lens in (the sample was Kodak Ektar 80mm/f2.8 for Hasselbald 1600F).

I've also heard that the UV treatment works only periodically, and the cleared element will fog eventually and become thus useless.

[rosko]

Some old versions of  Nikkors 35mm f/1.4 contain thorium in their optical elements.

If it was dangerous we certainly would know.

[Humboldt]

My issue with leaving lenses for UV treatment in the sun is not paying enough attention to the weather forecast and the potential for rain.

The risk for overheating the lens here in Gothenburg at the Swedish west coast is very low. During this time of the year the sun is as absent as water in a dessert - almost. Water in the form of rain on the other hand, is as common as the sand in that dessert.

[Humboldt]

Years ago, a Japanese photography magazine put out a special article on the lenses using thorium glasses.  They measured the radiation at Japan Atomic Energy Agency　Nuclear Science Research Institute.

The result was that the amount of radiation was roughly equal to that of natural radiation when you were a couple of meters away from the lens in (the sample was Kodak Ektar 80mm/f2.8 for Hasselbald 1600F).

Does it mean the radiation became twice compared to what it would have been with no lens a few meters away? Normal background radiation plus the lens at the top of that? Sounds like rather high levels if a single lens kept in a home doubles the radiation. Or is the background radiation very low in Japan?

I've also heard that the UV treatment works only periodically, and the cleared element will fog eventually and become thus useless.

Does this mean it is better to avoid UV-treatment completely? Is it the UV-treatment as such that cause the fog? Or is the fog unavoidable under all circumstances? Or is it just a rumour?

[Akira]

The amount of the natural (environmental) radiation varies depending on the area.  But the total amount of the radiation should increase for sure.

I would avoid purchasing such lenses in the first place before attempting the UV treatment...

[Bill De Jager]

My understanding is that the one health concern that made sense regarding thoriated glass was for use in eyepieces for optical instruments that might be used for hours at a time, day after day in occupational use.  That would be due to the combination of extremely close proximity, exposed eye tissue, and extended exposure.

Due to the inverse square law, even having the radioactive component in a camera lens 5 cm away instead of 1 cm results in a 25x reduction in exposure.   A distance of one meter means a ten-thousand-fold reduction in exposure relative to 1 cm.  I have a Geiger counter, and for my radioactive lenses there is no perceptible difference in readings at a distance of one meter vs. farther away.

One error you will see in some online discussions of this issue is the assertion that the radiation from thoriated lenses is all alpha radiation which has low penetrating ability.  While this is true for Thorium itself, this is not actually the case for these lenses since the decay chain from Thorium has gamma emitters.  Any thorium in a lens was placed there decades ago, and subsequent radioactive decay will have completely populated the decay chain by now since all radioactive isotopes in that chain are fairly short lived. 

I've confirmed the presence of gamma radiation by placing sheet metal between the lens and the Geiger counter.  The radiation count is still elevated even though the sheet metal will stop all alpha and beta radiation.

[Akira]

I suspect that the use of thorium glasses was not seriously concerned when A- and H-bomb experiments in the atmosphere was the common practice (in 1950s and early 60s).  Allegedly the environmental radiation was much higher then than today.

[Bill De Jager]

I suspect that the use of thorium glasses was not seriously concerned when A- and H-bomb experiments in the atmosphere was the common practice (in 1950s and early 60s).  Allegedly the environmental radiation was much higher then than today.

My radioactive Pentax M42 SMC Takumar 50/1.4 dates from the 1972-75 period, long after the vast majority of atmospheric testing had ended (the French and Chinese were the remaining holdouts at that point).

The biggest threat from aboveground nuclear testing for people far away was the widespread dissemination of particular radioactive isotopes such as ¹³⁷Cs, ¹³¹I, and ⁹⁰Sr that can bioaccumulate in living things such as people.  It's not that global background radiation levels were much higher, but rather that particular isotopes from these nuclear tests would accumulate in our bodies and provide constant and intimate irradiation that could be significant at a population level (cumulative cancer mortality) over decades. 

This testing was going on when I was in the womb and in my early childhood so it's of more than just academic interest to me - along with millions of others I was exposed to the highest global levels of certain isotopes during the most radiation-sensitive period in my life.  Most of this global exposure came from testing by the U.S. and the Soviet Union.  However, radiation exposure for populations much closer to and directly downwind from the testing was quite another matter and was far more serious for those populations.  In some cases people got short-term radiation poisoning in addition to the long-term health risks.

There's a discussion of radioactive lenses here.