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Is my lens radioactive? Asahi Pentax Auto Takumar 55mm f2

Discussion in 'Adapted Lens Forum' started by spilla, Sep 13, 2017.

  1. spilla

    spilla Well-Known Member

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    Got a good deal on this lens from ebay. Here's a link to the lens on the Pentax forum.
    Please login to view links

    I know some of these old Pentax lenses are radioactive, couldn't find info online about this one specifically.
    The glass is slightly yellowed, not sure if that's just age.

    Any info appreciated, thanks!
     
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  2. fugu 82-2

    fugu 82-2 Active Member

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    It probably is radioactive; the one I have is, but not terribly. The radioactivity is from the thorium tetrafluoride anti-reflection coating they used then.
    My red Fiestaware is a lot more radioactive than any of the old lenses I have.
     
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  3. pfogle

    pfogle Puzzled

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    The only 'radio-active' lens I'd heard of from Pentax, is the older SMC 50/1.4, so I googled it and found Please login to view links.

    If your model of lens is radio-active, it's unlikely that the level will be measurable in normal use - the radiation is from Thorium in the glass, which is an alpha-particle emitter. These particles cannot pentrate skin, and in fact, are stopped by a sheet of paper. The only way you can get any radiation is by direct physical contact with the glass (the particles have a range of 10s of centimeters in air, but since the radio-active element is at the rear of the lens, it's most unlikely to get out).

    The yellowing of the glass is caused by microscopic defects in the glass from the alpha particles emitted inside. I believe you can cure it with UV light (like several days of direct sunlight).
     
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  4. beakhammer

    beakhammer Premium Member

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    Please login to view links

    Here is a list of some radioactive lenses.
     
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  5. Alex Cremers

    Alex Cremers Premium Member

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    Mikaton by Zhonghi is also radioactive? :eek:

    A lot of people here have the Super Takumar 55mm 1.8 and it's on the list.
     
  6. ruby.monkey

    ruby.monkey Premium Member

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    We're not talking Radium Girls here. Old age will kill all of us long before the lenses do.

    The only problem you might have is a warm colour cast from the glass going brown, and treating the lens with UV light should fix that.
     
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  7. pfogle

    pfogle Puzzled

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    No, they use lanthanum, not thorium. A lot of lenses on the list have lanthanum glass - it's very common and has very low radioactivity. Thorium glass lenses are only a problem if the radioactive element is either the front or rear element of the lens (alpha radiation can't even go through paper, and is harmless to skin. You would have to inhale radioactive dust to be at risk).
     
  8. johant

    johant Premium Member

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    The SMC Takumar 55/1.8 is also on the list. I've had mine for a long time, and I wouldn't say it has yellowed at all.

    OTOH, my CZJ Sonnar lenses (zebra models) are very prone to yellowing.
     
  9. GregWard

    GregWard Premium Member

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    Oh yes - you should be really hugely and totally concerned. These lenses are complete killers. See this link if you don't believe me...



    ... or maybe - not so much!

    :p
     
  10. Alderney

    Alderney Well-Known Member

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    Just a note of caution on appearance. Super Takumars have a single coating. Light that reflects back from the front element (i.e. that does not go through the lens) will appear a light golden colour. This is normal and not the same as the yellowing from radioactive elements. My Super Takumar 55mm f2 (37107) has the golden reflection, but does not have the yellowing that is characteristic of thorium content.
     
    Last edited: Sep 13, 2017
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  11. Finder

    Finder Active Member

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    Not sure I would get medical advice from some random guy in the intertrons. Thorium was banned from eyepieces because it damaged eyes. Kodak Aero Ektars will fog unexposed film if you set them on it for long periods of time. These lenses would be technically be considered hazardous waste. Things do not have to kill you to be harmful. Would I worry about a hot lens in a draw somewhere, no. But neither would I take medical advice from from some snarky vlogger.
     
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  12. spilla

    spilla Well-Known Member

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    Thank you guys for all the comments so far. I would like to mention a few things.
    1. I'm a US board-certified physician in Internal Medicine. I have no specific expertise in radiation safety.
    2. I would not assume (as I've seen some post online) that these lenses are just alpha emitters, see this video as an example:

    3. My feeling is that anyone who owns a radioactive lens should know that it is radioactive, and take some precautions in storing and using it. As others have mentioned, I would not call the amount of radiation emitted (which I have seen estimated as 1 X-ray per hour at the lens surface) a minimal amount, and personally would not want it out in the open in a room I lived in, I wouldn't want it near my kids, and I wouldn't want it right up to my eye or body for an extended period.

    SO back to my specific lens -- As there is definitely some uncertainty, I bought a geiger counter and will measure it and get back to you all.

    - Scott
     
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  13. Finder

    Finder Active Member

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    If you don't have a Geiger Counter, (seriously, what household does not have a Geiger counter these days--have you watched the X-Files?) place the lenses under sun light for a few days. If the yellow is bleached, then it probably is a hot lens. And the yellow should be viewed through the lens, not the reflective surface, which could be coatings, as point out above.
     
  14. Zurubi

    Zurubi Well-Known Member

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    Couldn't get past 1/3 of this video, what a know it all guy!

    I disagree with the statement that new lenses are worst. We now can make aspheric surfaces and back then they couldn't...And there are other ways to make low dispersion glass.
     
  15. pfogle

    pfogle Puzzled

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    Unfortunately, the person in the video is a believer in pseudo science and a conspiracy theory fan (I quote "light is not a particle, anyone who tells you that has been sucking on the cancer-stick of quantum theory"). Not all Fuji fanboys are sane! However, that doesn't mean I think everything he says is nonsense :D

    I don't know what the lens is that he's discussing - it looks like a Kodak Aero Ektar (anybody?) and they did have a reputation for being hot in their day. As to the radiation, I was wrong to say the thorium glass only emits alpha particles - the thorium does only emit alphas, but the decay product (radon 228) is a beta emitter, as is its daughter, actinium 228. So, sorry about that. As the half-life of thorium is millions of times longer than the daughter elements, I would expect the count from beta to be approximately equal to the counts from alpha, which is pretty much the impression I get from his impromptu experiment in the video (about half the intensity of radiation detected when the lens is under the table).

    Personally, it's not something I worry about, but I can sympathize with those who feel uneasy. Getting a detector would be interesting, but how to interpret the result is something I wouldn't be able to comment on (I do have a degree in physics, and I've worked in a nuclear lab, but these things are complicated and I'm no expert). From what I've read, the '1 x-ray equivalent per hour exposure on direct contact' is roughly the figure out there - something like the extra radiation you'd get crossing the USA in a jet.

    The fact that a lens can affect film is to do with the fact that film is a very sensitive detector of radiation, and that a lot of thoriated lenses had the thorium in the rear element, so the radiation would be highest inside the camera.
     
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  16. RnR

    RnR Member

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    Obligatory xkcd link - Please login to view links

    If you are worried about a old lens being in the same room as yourself, you should not be eating banana's, taking flights, or even live in a concrete/stone/brick house.

    Flight from LA to New York is 40 uSv. Chest xray is 20 uSv. Yearly dose from naturally occurring Potassium in the body is 390 uSv. Normal yearly background dose, ~4000 uSv. Lowest one year dose clearly linked to an increase in cancer risk is 100000 uSv.

    Fondling an old 'hot' lens for several hours (lets say 3 hours) once a week would nearly double the normal yearly background dose. And that is assuming full contact during the entire time and assuming the '1 x-ray equivalent per hour exposure on direct contact' rule is referring to a chest xray (20 uSv) radiation dose. It could be referring to a dental xray (5 uSv) or an arm xray (1 uSv) which would dramatically reduce the yearly dosage associated with a full blooded love affair with a 'hot' old lens.

    Nothing to fear really. IMHO ofcause :D

    Edit: A Konica 57mm f1.2 has been measured to be around 4-5 uSv/hr according to a Please login to view links. This is much lower than the chest xray value I used above. So I have absolutely no issues in regular usage of this fine lens, nor any issues in looking at it lovingly when I am in my office where its stored on a shelf. Sleeping with it every night, spooning it tightly to my chest is out of the question however. A less radioactive object have booked that spot :D
     
    Last edited: Sep 14, 2017
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  17. lawsofphysics

    lawsofphysics Premium Member

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    Thorium
    There is no reason to assume an anything. The TH-232 radioactive-decay chain is not a mystery. This US government Please login to view links summarizes the process.

    The major emissions are alpha and beta particles. Both interact with matter and (such as glass and metal) and the resulting lens element exposure from ionizing radiation is low. In fact, ~3mm of aluminum is an effective shield for beta radiation. Still, beta particles penetrate about 100 times more than alpha particles. So beta particles are the primary source of concern.

    Decades ago eye damage was reported from TH glass in optical eye-pieces. This does not mean lens glass is equally dangerous (unless you dismantle the lens and place the glass next to your eye repeatedly).

    It turns out TH-232 decay products also emit gamma radiation at very low levels. In fact, some gamma-ray spectrometers can not detect Tl-232 decay products. Gamma radiation from one lens is not a health concern.

    Unless the lens breaks and the TH glass is shattered, the health risks seem low. But the risks are higher than non-TH glass. Thie issue is how much higher.

    When you get your Geiger Counter, place piece of paper between the lens and the detector.
     
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  18. spilla

    spilla Well-Known Member

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    UPDATE: Asahi Pentax Auto Takumar 55mm f2 is NOT radioactive.

    Not sure if there are differences between copies, but my copy had not a blip.

    Thanks for all the comments.
     
  19. Alderney

    Alderney Well-Known Member

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    Hello spilla;
    Each run of Takumar lenses has a "product code" number on the back of the auto/manual switch.
    Do you mind telling us the number on yours?
    Mine is 37107 which means it was manufactured in 1973-75. It's the kit lens that came with my Spotmatic 500.
    The numbers for the various versions are on Please login to view links
    Thanks.
     
  20. gyoung

    gyoung Premium Member

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    I got one of these with my S1a in '63, a lovely lens. And although I part exchanged that one for an M3 I later bought another S1a with 55m/2 which is sitting up in my cupboard since 30 years and it hasn't started glowing yet.
    I often wonder if there is really any optical difference between it and the 55/1.8. Or just engraving!

    Gerry
     

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