Probably depends on the lens...
I have a 24" aerostigmat where the rear element is supposedly as high as 30% by weight of whatever thorium component was used. From what I understand the 50mm takumars used a lower percentage. Also, the rear element of the 24" F6 is a little over 4 inches wide, and about an inch thick, so there's quite a bit more stuff there to emit Gamma, Beta, and Alpha particles. Some lenses used lanthanum as opposed to thorium, which does not emmit the more dangerous gamma radiation, jsut beta and alpha from what I understand. Someone (a radiation saftey officer who worked at a powerplant, can't find the link offhand) tested the AreoEktar (Aerostigmat?) 6 inch F2.5 and found that the radiaotion level 6 inches from the rear element was slightly higher than the "safe level" for prolonged exposure required at his plant, so basically, so long as you didn't sit on it for months, your future generations would be just fine. If I ever get my university buddies at the local physics lab to test my lens I will post the result. I might be slightly worried about it if I had one glued to my eye 12 hours a day 5 days a week.
For the record, I smoke, drink, drive a car with no airbags, I really don't think using my slightly radioactive lens is even on the top 100 list of things that's going to kill me. Pretty sure "murdered by jaded lover" or "accute toxicity to fixer" both have a higher probablility of landing on my death certificate.
Imagine the stories we coul tell the ladies.......
Originally Posted by mhcfires
Anyone here redo their kitchen recently? Did you put in granite counters? Try googling granite counters and radiation. Seems to me, someone will always find a way to tell you something is bad for you. Incidentally, what's the latest on soy? I've stopped paying attention to that one too.
Originally Posted by Ralph Javins
I'm not sure I'd sleep with an aero-ektar under my pillow, and maybe I'd be reluctant to store it anywhere other than the basement (if I owned one), but I realy doubt a slightly radioactive lens is going to be the thing that kills me (I live in NJ after all)
The check function is purely electronic and verifies if the meter responds to a current. Whether the GM tube is still functional and will generate a current is anyones guess without an actual radioactive source emmitting gamma rays which is what most of these GM counters were designed to detect.
Originally Posted by One_DaveT
In any event, this Thread is a 'Tempest in a Tea Pot'!
The NRC only regulates emissions from Power Plant and other facitlties that it has jurisdiction over. Your granite whether or not it has some low level of radioactivity is beyond its Regulation as are your lenses.EOT-Dick
BTW FWIW a Scintillation detector is NOT a high sensitivity GM detector.
A GM detector works by counting a pulse from a gas discharge breakdown when a particle with sufficient energy enters the GM tube. A Scintillation detector records the light pulse from a particle interacting with a crystal of material that gives off light.
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I remember reading, years back, that the real risk with using thorium in a lens is in the manufacturing phase. I guess thorium dust in the factory (grinding phase of lens building) can pose a significant and real health risk to the worker.
With respect to Nikon lenses having thorium, it was, IIRC, only the early multicoated lenses, like the Nikkor-N 35f1.4 and Nikkor-N 28f2.
The 50f1.4 Nikkor-S is only single coated, and just happens to have a brownish color tint to the coating. If you hold one up to your eye, then look at a light source, it's perfectly clear. A 35f1.4 Nikkor-N, that is yellowed, not so much. It'll actually look yellow from the thorium.
I had one of the early 35f1.4's, and it was a decent lens, just got tired of using a Nikon B8 filter to correct for the yellow tint, while shooting daylight balanced color film. I guess I could've just shot tungsten balanced color film with it outdoors, then had normal looking photos...
If I ever come across another early 35f1.4 that still has normal colored thorium glass in it, I'll grab it, and use it just like I do my other Nikkors. Really not that big a deal to me.
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I see that this subject brings so much passion here, even on an rather civilized place like APUG
I am suprised too, to see so much unargumented, unchiffred point of views, and so much "the man who saw the man who saw the bear" stories (I don't know if this french expression translates well into English)
To be straight, I owned and I own several radioactive lens, and a (recent/calibrated) radiameter (Geiger counter), so I know *de visu* what is the point.
The top winner is an old Super-Takumar 105 mm f/2,4 (for Pentax67), where the rear cell read at contact about 1500ÁRem/h (micro-rem by hour) or using the normalized unit 15 ÁSv/h (micro-Sievert by hour).
I had to borrow another radiameter from a friend to measure it, since mine was saturated ! (Max is at 999ÁRem/h).
This measure should be taken for the two type of radioactivity, beta AND gamma. Because gamma radiations are emitted by this lens too. Beta radiations are stopped by any screen, even by the human skin. But Gamma rays are another story, a few millimeter of solid matter are virtually transparent to them. I still measured about 600ÁRem/h through a 5 mm thick lead sheet, in contact.
To make comparison, I measure next 20ÁRem/h in my basement. This measure is more than the outside in open air (a few ÁRem/h), because I live in a granite walls house, in an granitic ground region. So why bother about granite sink ? . So we can state this SuperTakumar is almost one hundred more radioactive than natural background.
I found the Pentax 50mm f/1.4 (for 35mm camera) Super-Takumar was radioactive, too, about 300/400ÁRem/h at rear lens. I think it's the same glass which the Pentax 67 Takumar used, but the lens is much smaller in 35mm, too.
I tested three of them, and the three was hots
A good clue for a *possible* radioactive glass is a certain brownish cast increasing with age, under a certain incidence. Don't mix up it with yellowing of aged optical glue, which can occurs with older lens.
The better way to see it to hold the lens in front of a white sheet of paper. It's less visible if you look at a light source.
In my "horror box" I have too a German lens (from a well know maker , where the rear lens is radioactive (but much more lesser), and the front lens of a well know French camera. And no, NONE of my russian lenses are radioactive (and I own a good number of them)
A notion that should not be forgotten is that radioactivity decrease like light, in inverse square law of distance. For example, the 67 tak radioactivity is indiscernible from the background at 60 or 70 cm of distance.
So, dangerous, or not ? An arbitrary safety limit, in Europe, for the civilian people was put at 1mSv/year (100mRem/year). So, with a rough calculation, you should be *in contact* with the above Takumar about 66 hours to exceed that yearly safety limit. So, don't sleep with one of these under your pillow Or even on your bedside table.
Yes, when you expose yourself to radiations, you'll take an increased statistical risk to develop a cancer, but when you smoke too (IMHO, a bigger risk), when you are X-rayed at the hospital or the dentist, or even worse, if you receive a PET-scan, or when you take an high altitude transatlantic flight (cosmic rays), etc, etc.
It's each to his own, to decide if this risk should be taken (and added), nobody should be blamed to take on side or the other
The better work I know on the net, about gamma lenses was made by Michael Briggs, on a rational, depassionated way :here
An interesting image, about film fogging, can be seen in this thread
Sorry for this lenghty post, and sorry too for the many probable english mistake.
This is an excellent and informative post, Raphael. What you have noted is all I was trying to point out:
"The top winner is an old Super-Takumar 105 mm f/2,4 (for Pentax67), where the rear cell read at contact about 1500ÁRem/h (micro-rem by hour) or using the normalized unit 15 ÁSv/h (micro-Sievert by hour).
I had to borrow another radiameter from a friend to measure it, since mine was saturated ! (Max is at 999ÁRem/h)"
"So we can state this SuperTakumar is almost one hundred more radioactive than natural background."
I am glad you have discussed this matter in an in-depth manner, as no one seemed to believe me when I had tried to explain that there is more than "a little" radiation in some of these lenses. I agree: for some this may be tolerable, but others are not "irrational" for being concerned and cautious and thus avoiding these lenses.
LOL, all those people who are worried about radiation of thorium show that they don't have the slightest clue how radiation works. Take a geiger counter and measure the inside of your house, then measure the lens, It might not even be detectable trough the background radiation you receive every single moment of your life. Also, the particles it emits are Alpha and Beta particles, while Beta particles are a little more powerful they cannot go trough things like thick lens glass, nor can the alpha's. Both particles are only dangerous when they float freely in the air as dust.
Keep in mind that people can have far more dangerous substances in their homes. Remember those old vintage wall clocks that glow in the dark?? well if they are old enough (like WWII area or just beyond that) they most likely contain Radium, and that dear people is a real Gamma emitter!! Far more powerful and dangerous then Thorium used in lenses. I have 2 tabs (which they used to place above the light switches in the 1960's to see the switches in the dark) filled with Radium and while the emissions don't go very far (I use them to test Geiger counters that are part of my NBC collection) I don't want that to float around in the form of dust (the Radium in the tabs I have are safely sealed in Plexiglass). The most dangerous part of radioactivity is when it's released in the form of dust, then it can get everywhere, when it's in the glass it can go nowhere.
Sure, I could give you a boring explanation who I really am but I rather let the Origami do the talking.