Radioactivity of some manual lenses

One of mflenses forum member had test for some radioactivity in some old manual lenses.

Here is the discussion :

Its serious because we know that lens lovers tend to spend a lot of time near our jewels – we don’t only use them when we go out to photograph, we handle them, clean them, like to have them near – sometimes when I like to relax without sleeping I take a couple of my lenses and look at them, I like to feel them in my hands – stupid I know But to do it with a lens that is 10 times higher than background RA might not be safe.

Nox gave us the comparison term, it’s the background radioactivity level. It surely depends on the area where you live but I think we can assume that on average, the values of where you live should be similar.
Nox lists background level at about 200. The SMC Tak 1.4/50 is almost 2000 which means 10 times more the background level.
I would not feel safe to have around all the time something that is 10 times more radioactive than normal.
To use it for a photo session is one thing, to have it near where you seat or sleep is something different.

I prepared a test of radioactivity on majority of my lenses. Here is the result:

I made measurement for both rear and front elements (1cm distance, if possible). Some results are as expected, but some of them are a bit surprising for me:

S-M-C Macro Takumar 50/4: radioactive… VERY low intensity, but present. I think it uses lanthanum glass.

Super Takumar 35/2.0 V1 / PRO (the big one)… low radioactivity, half than on the later version, which is known to be thoriated… this level of radioactivity could mean utilization of lanthanum glass or very low amount of thorium

S-M-C Takumar 85/1.8: I have never seen this lens in any list of radioactive lenses, but its radioactivity is really evident. It’s very untypical, that front side radiates more than the rear one, so the thoriated(?) element is located in front optical group…

Carl Zeiss Jena Biometar 80/2.8 (zebra, P6): next surprise… while the old M42 (alu) version isn’t radioactive, the newer one (for medium format cameras) is. Radioactivity level is really low. It could be lanthanum glass or very low amount of thorium…

I made some colored highlights to allow easier orientation… blue = low radioactivity, red = high radioactivity

I must say, that the results aren’t 100% exact (cheap dosimeter, I have no idea, what aspects can impact the measurement etc., accuracy is at best 20nSv/h – very likely lower), but I think, that all colored results really stands for radioactive glass.

I also found informatio, that both thorium and lanthanum glasses were developed in time and it became so pure, that its radioactivity was almost non-existant. It means, that even non-radioactive lenses can be equipped by thorium/lanthanum elemens.


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