[John Kovarik]

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.....I just bought a SupTak 28/3.5 from a guy in Santa Fe. His pix showed dust on the lens...when I asked if it was fall-out from Alamagordo, he said no, from
Los Alamos and the radiation is free........I also have a SupTak 50/ 1.4 on the way.........I'll be 'glowing' with satisfaction when I get them...............

[borno]

I'll bet this bad boy is smokin' Pentax Ultra Achromatic Takumar f5.6 300mm UV lens - (eBay item 120162954566 end time Sep-27-07 09:21:11 PDT)

[alexfoto]

Articolo nadir
Articolo

Radioactive lenses

In the past to obtain some benefits from the optical or to problems of imperfect refining there was present some radioactive element on some old lens.

I think could be interesting add this information on any old lens.

I'm interesting in old lens because they are good and cheap (despite in Italy is different ...) but i would like known if there is that big problem or not.

Note:
You could use the google translator for the italian articles.

Clear could also add other articles.

I just checked what our national radiation protection agency (Steilyturvakeskus (STUK) Strlskerhetscentralen (STUK) Radiation and Nuclear Safety Authority (STUK)) has to say about this. The translation is mine (and probably bad):

Thorium has sometimes been added to glass to increase the refractive index, to reduce surface reflections and to color the lens surface. In the US some lenses have been found to contain thorium up to 30% of weight. A large television camera containing such lenses has been measured to radiate 30 µGy/h of gamma radiation and 100 µGy/h of beta radiation at lens surface. The effective dose rate for a person 50cm from such a lens has been estimated to be 10 micro Sieverts per day.

Eyeglass lenses have had small amounts of natural radioactive material such as uranium, thorium and some rare metal salts. There are reports that in the 1970s in the US there were thorium-tinted lenses that were found to cause the corneal surpace cell layer of the eye a dose rate 0.1–0.3 mSv/h, from beta radiation in the depth of 2mm a dose rate of 0.7–2 µSv/h and from gamma radiation a whole eye dose rate of 0.06–0.3 µSv/h.

These numbers won't probably apply directly to a DSLR lens and its normal use.

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Last edited by emr; 07-29-2009 at 07:11 AM.

[forensicscientist]

while I cannot guarantee the "tint" of the glass, I'm happy to make anyones lens as radioactive as you'd like Heck, I'll make your camera body radioactive too! No charge!

[K-9]

Would a radioactive lens do anything to the sensor or the ICs? I don't know how much radiation these things put out.

I'm not so sure they are "active" unless ground up. I don't think they give out any radiation in their current state. You would have to grind up the glass to dust and even then, I don't believe the dust can be absorbed through the skin. It would have to be consumed or inhaled.

So, unless you're licking your tak's elements, or making takumar stew, you're probably ok exposure wise.

[jstevewhite]

I'm not so sure they are "active" unless ground up. I don't think they give out any radiation in their current state. You would have to grind up the glass to dust and even then, I don't believe the dust can be absorbed through the skin. It would have to be consumed or inhaled.

So, unless you're licking your tak's elements, or making takumar stew, you're probably ok exposure wise.

Nah, they'd still be radiating. Thorium is radioactive until it kicks out the particle jams, becoming not-thorium - maybe radium? Here's the thorium decay chain:

Th-232 decay chain.

Highly radioactive substances (like plutonium) are *much* more dangerous when ingested and lodged in the tissue where high doses of radiation can affect cells over time, but radiation itself causes all sorts of bad things, even if you don't ingest the radioactive substance.

[K-9]

It may degrade slowly and still be emitting radiation, but those emissions can't penetrate your skin, so I would say it's still safe. That is of course, unless you're a lens licker. Thankfully, I kicked that habit a while back.

[stevebrot]

It may degrade slowly and still be emitting radiation, but those emissions can't penetrate your skin, so I would say it's still safe. That is of course, unless you're a lens licker. Thankfully, I kicked that habit a while back.

I don't know if the thorium in a lens constitutes a health hazard, but I do know that the yellowing lens is a result of the affect of the radiation on the resins used to cement the lens elements together. The glass itself remains clear. The exposure to UV light treatment bleaches the cement back to a more clear state.

Steve

(Thorium | Radiation Protection | US EPA)

[cwm9]

That is of course, unless you're a lens licker. Thankfully, I kicked that habit a while back.

What, you don't eat off red Fiestaware?

Fiesta Ware (ca. 1930s)

Red Fiestaware, with a radiation rate of _20_ mrad/hr (20x that of Takumars -- plus you EAT OFF IT!), if you ate off it every day, is estimated to result in the consumption of .21 grams of uranium per year resulting in a dose of 40mrem per year. (Note that rem is like rad, only adjusted for how bad the particular kind of radiation is to humans. Not all radiation is created equal.)

The safety limit for humans is 5000 mrem per year. A single CT scan, which I had earlier this year, delivers a whopping 1200 mrem in one go.

Just for comparison, SMOKING a pack a day is estimated to deliver somewhere between 2000-5000 mrem per year.

So, considering that the lens is 1/20 what the dinnerplate is, I wouldn't worry too much. Just don't leave the lens in your pocket next to your testicles for 5 years running, ok?

As to electronics, if you can deliver about 5000 rads over a few minutes you can do long term damage, or if you exceed around 1Mrad. Since the lenses are 1mRad (1/1000 of a rad) in an hour, I don't think the camera will notice.

Put another way, background radiation is about 300 mrad per year, or about 1 mrad per day. So when your finger is touching the lens (What are you doing cleaning a lens with your finger?!), you are getting about 25x the rate as when you are not touching the lens.

Also, the rate of exposure is an important consideration. Your DNA has the ability to repair itself when damaged, if the damage is not too extensive. If you break off a single base, a repair molecule comes along and replaces it using the base's pair (each point on the DNA has a pair of bases) as a reference. Then the DNA is as good as new. If the rate of exposure is higher than the rate of your cells ability to repair themselves, or if you just get unlucky and get a full break, THEN you have a problem. If you received your entire lifetime dose of radiation all in half a second you'd probably be in a serious world of hurt, even though that same dose spread out is unlikely to cause problems.


The major danger from these lenses is not from using them, but from breaking them and then inhaling or ingesting radioactive dust. Don't do that. Now you are asking for trouble. The people who smashed the Takumar as a way to "fix" the lens were doing something stupid. I hope they didn't breath in too much of the resulting junk. http://www.hermes.net.au/bayling/repair.html step 3 = NO NO!