Which Spotmatic lenses are radioactive?

Discussion in 'Classic Manual Cameras' started by andy m., May 16, 2004.

  1. Could anyone possibly tell me which Spotmatic lenses are most likely
    to be radioactive? (I'm mainly interested in 50mm).

    I have tried to search but can't seem to get a clear message from
    the Google results.

    Thanks, Andy
  2. It seem that Thorium was added to some lenses up until the 1980's. Doesn't seem like that much of a risk, but see the following link for additional info.

  3. In the 'Annals of precision engineering and optics' (a german edition) it was stated in the early 60s that Thorium was already replaced with lanthanum which - as a glass alloy ingredient - has similar properties as thorium but a much smaller percentage of radioactive isotopes.

    In this book there are also excerpts from the Schott optical glass catalogue which does not mention any thorium glass but several makes of lanthanum glass.

    Probably none of the Spotmatic lenses contains thorium.
  4. Does the radiation tend to expose the film over a long period of time?
  5. I don't have the list, but I recall the first time I ran across this being amused that my Super Takumar f/1.4 50 mm was on it (there's a range of serial numbers with the thorium glass). I've had this camera and lens since 1981, left it with film loaded for extended periods on a couple occasions, and never seen fogging. I'm no radiation expert, but it seems to me that a lens that doesn't fog ISO 400 film is probably no hazard to the operator in normal use. I wouldn't recommend using one as a telescope eyepiece (which was the discussion in which I learned I had a radioactive lens), because that involves putting your eye very close to the front element, potentially for hours at a time -- but for normal photographic use, I wouldn't consider it any more hazardous than, say, an Auto Rikenon f/1.8 55 mm -- which is not radioactive, and weighs about the same.
  6. This has been posted before but it's always good for a chuckle....

  7. There's a screw-mount 50 mm f1.4 Super-Takumar that is radioactive from thorium. I have measured the radioactivity from one. The measurements prove beyond any doubt that the lens is radioactive from thorium, so ignore any arguments based upon published info that implies that it can't be so. I speculate that this might be the most common lens containing thorium.
    I am not an expert on Pentax lenses so I can't explain which 50 mm f1.4 model has the thorium. One that I measured has a serial number just above 2,300,000. The label has "Super-Takumar 1:1.4/50", it is screw-mount, and it has a MAN/AUTO control. The ones that I have seen can have had a conspicuous discoloration to a color like tea. Some call it yellow, I would call it amber or brown. If you see the color, it probably has thorium. The color can be cleared with exposure to UV light, so the absence of the color doesn't prove the absence of thorium.
    Thorium in lenses is much more common than most photographers realize. Thorium glass was used into the 1970s, for example, in the 35 mm f1.4 Nikkor (see http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0054IM). Almost every major lens manufacturer has used thorium glass. I think there are some German lenses past the early 1960s.
    I have some info on thorium glass on my Aero-Ektar webpage: http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html. Two other recent photo.net threads on thorium glass: Should I be worried about these lenses? Radioactive? Help. at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=007l93 and Aero-Ektars: Does UV light remove the brown stain? at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005obo.
  8. Many thanks for all the answers. A
  9. good one ! Kevin .. LOL ... pc
  10. A bit late, but...

    As far as I know, three Takumar lenses are aradioactive. The 50/1.4 is one of them. There also is the 35/2, at least the older version with the large front element. The rare 17 mm wide angle lens (not the fisheye) is also said to be radioactive.

    The radiation level is so low you can simply dismiss it. I personnally tested a 50/1.4 Takumar with a meter. It reached about twice the value of the background radiation level of the lab, ie, the radioactivity level of a normal, "built" environment. Testing the 50/1.4 and normal garden grade earth would probably give the same results in most parts of the world.
  11. Late maybe, but much appreciated. Thanks, A
  12. Well, it looks like the Chicken Littles are at it again. Just the mention of radioactivity sends them into the galloping fantods. It has been established by competent authorities that those lenses with Thorium glass present no health threat under normal use situations. The coloration effect vis-a-vis lenses could be significant depending upon the length of exposure. X-rays, luminous instruments, cathode ray tubes, and other things regularly encountered in daily life exhibit radioactivity levels greater by several magnitudes.

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