50mm Lens Comparison – Radioactivity

18 thoughts on “50mm Lens Comparison – Radioactivity”

  1. Well done! Kudos to your thorough approach ๐Ÿ™‚

    I’m curious though.. in regards to the Takumar,
    if a rear lens cap absorbs 40%. of the radiation.
    What of a camera body, could it absorb twice
    as much or in fact all of it?

    Because I imagine this is a more common scenario
    for such a lens, unless of course one carries a zillion
    lenses along on photo excursions.


    1. Hi Eva.
      The absorption of radioactivity depends on the density of the material (that’s why lead is so effective at this).
      Of course, a camera body with several layers of plastic, glass or even metal in-between lens and photographer is bound to reduce the level of radiation more than a simple lens cap would.


    1. Hey, funny that you should ask ๐Ÿ™‚

      I just measured it this week and it’s definitely radioactive. Radiation is mainly emitted from the rear element and it’s not as intense as the Takumar, but still quite impressive.
      Really didn’t see that coming.


    1. I’m fairly certain that none of the 35mm format Pentacon branded lenses are radioactive. You could always measure it with a Geiger Counter. Take it to the physics department of your (or your kids) school/University and let them quickly measure it. Takes 1 Minute to do so and you’ll have absolute certainty.

      Be advised, however, that everything has a certain amount of radioactivity to it, so a measurement of 0 (mSv, R, Bq, etc.) would be a device error.


  2. @danielpetessondemo
    Hey 0.13 ฮผSv/h is 0.00013 mSv/h, which is about the same as I measured for background radiation in our physics department. That means the lens has not been manufactured using any radioactive glass.

    Truly radioactive lenses will be 100 – 1’000 times more radioactive at close distances (3cm from the glass surface)


  3. Very nice and detailed article. I own the Carl Zeiss Jena Flektogon 35mm 2.4 Electric MC. Do you know if it is radioactive? I am asking because I am really worried with the old radioactive lens and I would like to know if what I have is radioactive. Thank you in advance.


    1. Hey Giannis

      Thank you very much for the praise.
      With regards to your lens. From what I could find, only the predecessor (f/2.8 version) of the 35mm Flektogon was radioactive.

      Does the glass appear to be yellow when you look through the lens at a white wall? If not, it most certainly doesn’t contain any radioactive glass.

      Otoh, you shouldn’t worry too much, since the radioactivity emitted by these old lenses would only be dangerous to our eyes if we used them as magnifying glasses for long periods of time.



  4. Hi, nice tests. I was wondering if the radioactive particle counts per minute are this high, does it effect picture quality in any regard? Would be nice to compare pictures made in the dark using radioactive lenses vs non radioactive. I believe the radioactivity might cause more noise in the pictures with higher ISO settings.


    1. Hey
      Thanks for the feedback.
      The radiation does impact photographic film, since it reduces silver ions in the emulsion if left exposed for long enough. This results in a “brighter” image, but not during your everyday use. You’d have to leave the film advance lever in the same position for a few days, I guess.

      If I can get my hands on a Pentax some day, I’ll try it, since I still have many rolls of unexposed acros 100 to shoot.

      Regarding the sensor: I doubt that the radiation has any impact on the sensor.
      First of all, we’d need to figure out whether the particles are registered by the sensor at all, since most of the radiation isn’t electromagnetic waves, but particles, and the gamma waves most likely pass through the sensor undetected anyways.
      Secondly, even in candle light, the number of photons is much greater than the number of gamma quants emitted by the radioactive glass. But the physics and math behind this elude me right now, so I can’t give you any numbers.

      Sorry I couldn’t be of any help here.


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