Collapsible Summicron, how radioaktive is it again...?

I have no idea where this chest x-ray equivalence is coming from, but this is non-sensical. As pointed out by Saganich, this would be something like 2.5 rem/h (and that would indeed have an effect, like radiation burns etc.).

By my best estimate (using various tables published by Oak Ridge National Laboratory), 5000Bq of thorium-232 translates to an annual dose of 0.1-0.2 mSv (yet another unit for dose, but this is SI, 1 Sv (Sievert) = 100 rem) assuming that you press this thing against your body w/o lens cap, front element to skin 24/7 for 365 days.

For comparison your annual natural dose is around 3mSv. Any reasonable use of this lens will result in a dose at least 100-1000 times lower than what you are exposed to just by being alive.

Thus, it is not surprising to find the following in the regulations by the NRC (https://www.nrc.gov/reading-rm/doc-collections/cfr/part040/part040-0013.html)

(7) Thorium or uranium contained in or on finished optical lenses and mirrors, provided that each lens or mirror does not contain more than 10 percent by weight thorium or uranium or, for lenses manufactured before August 27, 2013, 30 percent by weight of thorium; and that the exemption contained in this paragraph does not authorize either:

(i) The shaping, grinding or polishing of such lens or mirror or manufacturing processes other than the assembly of such lens or mirror into optical systems and devices without any alteration of the lens or mirror; or

(ii) The receipt, possession, use, or transfer of uranium or thorium contained in contact lenses, or in spectacles, or in eyepieces in binoculars or other optical instruments.

Thus, at least in the US there are no restrictions on possession or trade of lenses with thorated glass, but making those lenses or extracting the thorium is regulated.

As an aside, the above NRC regulation also specifically mentions:

(3) Photographic film, negatives, and prints containing uranium or thorium;

So, if you plan to to do uranotypes, you're in the clear.

This seems like a whole lot of fuss over nothing. The little tags that people used to wear to test for radiation contamination use film; we use film. If it's enough radiation to fire a radiation detector in a day to indicate danger, it certainly wouldn't work for photographers to have a lethal lens strong enough to fog film in a day sitting right next to a piece of film for weeks at a time.

mdarnton said:

This seems like a whole lot of fuss over nothing..

Click to expand...

That may be true, personally I've never believed in the mythical stories, but there are a lot of opinions and none-factual statements out there.
Thanks to people like Saganich, Soeren and Fraunhofer, we get some facts and not further myths.

Depending on what place you are looking on the internet, these lenses are rumored to be almost self-glowing.
Heck, even before the internet, the tales and myths of these lenses could be pretty extreme.

Getting facts out is always very nice, since paranoia and myths needs to be cleared away.
- For example, the all-important difference between radiation at the surface, inverse-square law, the difference between the front and the back of the lens etc.

Personally I have never really thought the lens was dangerous, but all radiation-sources should be respected as a rule of thumb.

I found the answers to this thread to be very very interesting and enlightening and now, even google can find some actual facts for the next guy ^^

kb244 said:

Though the person I quoted said it was the equivalent of 7 (seven) chest x-rays for the one on sale.

Click to expand...

Take into acount that a lot of it is beta, its of the surface of the front element and the inverse square law

Oh btw
https://what-if.xkcd.com/29/

I'm sorry if I may have noted info non-sensical. I don't want to alarm any if the info I saw and interpreted is scientifically faulty. I just did a review best of listings past and it was from a seller in Rancho Cucamonga CA for a 50 mm summicron f2 collapsible s/n 1092732 described as extremely radioactive in the listing, which described his Soeks Docimeter reading to run 15-16 Usv/h, which stated in the listing was 75x more than normal background radiation of .2, or so. He posted a pic of the reading in the listing, too. What I reported earlier was my recollection in summary that our e-conversation resolved it to equate to numerous chest xray-worth of radiation (based perhaps via other unit measure?) to what was available on some database table for various medical X-rays. Included in the ad was pictured a device screenshot for a readout of "15 uSv/h" and the words "Dangerous Radiation Background" in a red colored field below the reading. Another photo shows the device to be a grey/yellow colored Soeks-labeled rectangular item sized a bit smaller than a vcr tape laid atop the front of the lens. Don't fault me, I chose not to buy it! Looking at a prior post (Saganich) I guess this lens is nearing the low-end 20usv lesser X-ray. So if you walk around Disney all morning with the camera on a strap, lens out, and your hand over it that'd be several small X-rays..?

What is that, Usv/hour? Do you mean microSv?

Could I induce some hysteria on the WWW by asking what is the critical mass of summicrons

That would be f1.5, though luckily for us, it only goes to f2

At f1.0, it would become a singularity and swallow the universe and everything in it, eventually collapsing time itself and start a new big-bang.

Be warned!

Helinophoto said:

That would be f1.5, though luckily for us, it only goes to f2

At f1.0, it would become a singularity and swallow the universe and everything in it, eventually collapsing time itself and start a new big-bang.

Be warned!

Click to expand...

That could have happened already, how would we know?