Warning, radioactive lenses!

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I was recently reading some previous postings and web articles about certain lens glasses containing radioactive elements, and wondered if any of my collection might be 'hot'.
Initially, I was more curious than worried, but after doing some tests, I'm now definitely worried, and I think my findings deserve wider attention.

I have a sample of a 7" Kodak Aero-Ektar, which is a lens that has a big reputation for being potentially radioactive.
However, all the articles I've read state that the radioactivity is mainly in the form of alpha emmission, and shouldn't give much call for concern, since alpha particles are quite low energy, and easily stopped by any solid object. I'm told that alpha particles can only penetrate about 40 microns into human tissue.
Anyway, to cut to the chase: I just got our radiation protection officer to run a geiger counter and a dosimeter over the Aero-Ektar, and he found that the rear element was quite hot, giving about 200 counts/second. Worse yet, we discovered that it was mainly GAMMA emmission, since even an inch of perspex and a steel plate hardly affected the counts at all. The active element used in making the glass is Thorium, and a quick check of the table of its decay products confirmed that they're mostly gamma emmitters, after about 6 years of decay.
Dosimeter readings showed that within 1" of the rear lens surface, the dose was above the limit allowed for monitored radiation workers, and only fell to the publicly allowable safe limit at more than 6" from the lens.
I don't think I'll be using that lens as a paperweight, or handling it too much from now on. By all modern standards, that lens would be classed as downright hazardous, and not to be used without protective clothing!
I'll be testing the rest of my lenses as potential gamma sources as well in the near future.

-- Pete Andrews (p.l.andrews@bham.ac.uk), June 29, 2001


Since infinity is 7" and it is safe at 6" and you are not going to carry it around in your pocket, I would not worry about it. Pat

-- pat krentz (patwandakrentz@aol.com), June 29, 2001.

So, if you put it on a camera, and lock the shutter open, will it fog the film?

-- Dave Mueller (dmueller@bellatlantic.net), June 29, 2001.

Pete, since the part of my brain which is nearest the gg doesn't work anyway, I suggest you don't use the lens anymore and send it to me. That'll be two pints I owe you. Dave.

-- dave bulmer (dave.bulmer@bl.uk), June 29, 2001.

There was an article about this 4 or 5 years ago in Shutterbug, I believe. It reported that Apo-Lanthars, certain early Takumars, and many other lenses are somewhat radioactive. A simple test is to leave the lens on a sheet of photographic paper in a darkroom for several hours, then develop the paper. Dark spots from radiation exposure will be readily apparent.

-- Ed Buffaloe (edb@unblinkingeye.com), June 29, 2001.

Is this only present in older lenses or in new ones as well?

-- Dave Anton (daveanton@home.com), June 29, 2001.

Is this only present in older lenses or in new ones as well?

-- Dave Anton (daveanton@home.com), June 29, 2001.

I don't know if manufacturers are trying not to use radioactive materials, but the rare earths like lanthanium, thorium, yttrium, etc. are quite useful in adjusting refractive indexes, limiting dispersion, and absorbing UV in glass--it may be difficult to find replacements for them. I did some searching and can add Konica, Zuiko, and Steinheil to the list of companies that used rare-earth lenses--as well as the f/2.8 lenses in the Stereo Realist. Probably all the major lens companies experimented with them at one time.

-- Ed Buffaloe (edb@unblinkingeye.com), June 29, 2001.


200 counts/second seems a bit high. You're sure it is not 200 counts/minutes. For LF, the other two "hot" lenses I know are Voigtlander Apo-Lanthar and Rodenstock Weitwinkel Perigon (1958 vintage, 130 mm/F12). Both contain Lanthanum. From personal experience, Apo-Lanthar and Perigon are wonderful lenses and will not expose films under normal usage. No worry. They are not hot enough. On second thought, I'd better send my hot lenses to NYU for a safety check-up. Thanks for the note. Regards,

-- Geoffrey Chen (DB45TEK@AOL.COM), June 29, 2001.

Gosh, I wasn't aware of that! Is that the reason my older Takumars for Pentax 67 are becoming encreasingly warm in color?

-- Paul Schilliger (pschilliger@smile.ch), June 30, 2001.

Pete: this is disturbing information indeed, and I wasn't aware of it in the least - and I'd used a Pentax 67 system with older lenses until recently. Am I safe in assuming that newer lenses are OK?

-- Michael Mahoney (mmahoney@nfld.com), June 30, 2001.

There is no form of "safe" radiation, any radiation is potentially harmful, having said that, most watches give radiation off, your television radiates too! To say nothing of magnetic fields generated by high power electric lines! No there is no reason to worry about using a lens which uses radioactive elements. The yellow coloration of some Pentax and other brand comes from old adhesive which binds the elements and getting old changes color, can be fixed.

Dont't worry, be happy!

-- Andrea Milano (milandro@multiweb.nl), July 01, 2001.

I was a little hasty in minimizing the issue but I believe that any "old" lens would have been reduced the radiation by now we talk about lenses which are 50 to 30 years old and I believe that modern technology and norms are so stringent that nothing as bad as that could be produced just in the name of low -dispertion! However, thanks for raising the issue!

-- Andrea Milano (milandro@multiweb.nl), July 01, 2001.

Hi Andrea! Thanks for the tip on Pentax lenses getting yellow because of lens cement. You say it can be fixed? Can you give me some information and tell me if the price of such repair is not prohibitive?

-- Paul Schilliger (pschilliger@smile.ch), July 02, 2001.

Radiation safety isn't something anyone should be offhand about, but all the information I have (thus far) says that the risks to human health from radioactive lenses are very small. The only occupational health hazard I could find was for the workers making the lenses and reports of eye damage from people spending long periods of time peering into rare-earth eyepieces on telescopes and microscopes.

Obviously Pete knows this, but it's worth pointing out that most western countries take radiation safety very, very seriously. If you live in Europe or the USA your local university, large hospital or town will have a radiological protection officer. If you are worried about a lens in your posession contact them - they will usually come and check things out at no charge, and even handle disposal in many cases.

I recently had to do this (I discovered a Cs calibration source when clearing my father-in-law's house) and asked the officer about the various famous 'hot' lenses. He was of the opinion that the risk was very low (provided you don't sleep with them under your pillow), and that if you did want to get rid of them, landfill was both legal (in the U.K.) and the safest option. The radioactive elements are safely encapsulated in the glass and won't migrate to groundwater, or form airborne dust, at a rate worth worrying about.

The Aero-Ektars are a little different from the most other famous radioactive lenses in that they are military items, first designed and produced in wartime. They were designed to be used 'properly' and not by Joe Bloggs civilians who would sellotape them to the cat for a year and then look around for someone to sue when the cat died of distemper. It is therefore possible that these lenses in particular could be hotter than normal, quite apart from the fact that standards have changed quite a bit since the 1940s.

There is a lot of conflicting information about exactly what was the radioactive element(s) in these lenses floating round the internet, but Thorium and it's decay products are certainly part of the mix. Unfortunately my 7" Aero-Ektar was in Sweden when I was chatting with a fully-equipped radiological bod in East Anglia, so it's still an unknown, waiting in the cellar for my local expert to get back from sniffing round the sunken submarine reactors on the bottom of the White Sea. When he does so, we plan to do some gamma spectroscopy to find out just what is inside the lens. I'll report back once I have some data.

Incidentally, the fact that the rear elements of these lenses is usually yellowed all the way through is a pretty good indication that gamma emitters are involved. The change of colour will have also changed the refractive index and dispersion of the affected elements, so it might not work as well as it did when new anyway. In any case, unlike other aero lenses, the Aero-Ektars were designed for maxmimum brightness, not ultimate sharpness, so they're best kept for applications where a large aperture is required. They are the ultimate bug burner :-)

-- Struan Gray (struan.gray@sljus.lu.se), July 02, 2001.

I'll try to answer as many points as I can.

Pat. Such gung-ho attitudes to radiation are all too common among radiation workers, but they go quiet when one of their colleagues contracts Leukemia or some other lymphatic cancer.

Geoffrey, I'll check again, but I'm sure it was 200 counts/second.

The previous postings I've seen on this lens all assert that the radiation is in the form of Alpha particles, and if that had been the case, then I wouldn't have worried, since a piece of ground glass, and the body of the lens itself would have stopped it. What we found was that the radiation was definitely mainly Gamma emission, and this is much more energetic. It passes almost unimpeded through most things, including the human body. Deep penetrating radiation like this is much more hazardous to health.

The Aero Ektar used Thorium, not Lanthanum in the glass, and this is the reason why this particular lens is such a 'hot' property.
I'll investigate lenses containing Lanthanum, if I can get hold of any, but I don't think they'll be as bad.

As someone else pointed out. There's no such thing as a safe dose of radiation. The probability of radiation causing a malignant mutation of a cell in the body reduces with the dosage, but the chance is still there, even with a declared 'safe' level.

My radiation savvy friend's reaction was "I wouldn't sit on that lens for any length of time, if I were you". Meaning that it was 'active enough to cause sterility if placed close enough to those 'sensitive' areas of the body for long enough. Now, while that scenario is pretty remote, it's not impossible that I would quite happily have handled and used that lens taking absolutely no care whatsoever, if I wasn't aware of the danger.
It's not the radiation hazard itself, it's the fact that it can be there without your knowledge that's the real danger. Once you know about the problem, then you can take the appropriate precautions. (For example: I used to keep this lens on top of the fridge that I store my film in, and I now know that this wasn't a good idea!)

I don't think that any modern lens would ever be allowed out of the factory if it was as potentially hazardous as this particular old Aero Ektar, but who can say for sure?

I don't think there's any definite link between the yellowing of an optical glass and it's radioactivity. The two aren't necessarily tied together, but it's probably worth checking out.

Finally, I'm not trying to be scaremongering over this. I'm just trying to convey my own surprise and concern at what I found in one particular sample of an old lens. It also seems to me that some of the previously published articles playing down this problem might have been a little too frivolous.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 02, 2001.

Yellowing or browning of glass is a classic symptom of radiation damage, although in some cases a glass can be bleached if it was coloured to start with. Unscrupulous diamond dealers use X-rays to turn diamonds pretty colours for unwary 'fancy' collectors.

I have heard tales (good reference I know) of glovebox windows turned dark brown by radiation over the years. Usually this takes place at "a lab in Siberia", but Windscale is another popular destination.

Joking aside, it makes sense to find out as much as you can about the risk. It is also worth relating the risk to things like a daytrip to Aberdeen or using a Bluet camping light (thorium in the mantle). There are some jobs where you need that f2.5 aperture.

Incidentally, when my father in law was clearing *his* father's house, he turned up a phial of radium (Run away! run away!). It turned out that his father had chosen to repeat the Curies' experiment and isolate Radium from pitchblende as his school project. Times have changes somewhat methinks.

-- Struan Gray (struan.gray@sljus.lu.se), July 02, 2001.

How scary! Your way of talking off-hand on the subject just adds to my anxiety. I have been sleeping for ten years with a bag full, among them two or three of these warm amber babies in my bedroom. Shall I consult an oncologist or go directly for the mute? Kidding set aside, are they any precautions worth taking?

-- Paul Schilliger (pschilliger@smile.ch), July 02, 2001.

Just minimise the time spent with the lens close to your body. If you're not really close to the lens elements, gamma rays fall off in intensity with an inverse square law just like light, so the further away the lens is the less it can irradiate you. Don't keep it under your bed, or on top of your film safe. Pack it in your rucksack away from your body, not up against your spine. If you are sharing a tent or a bivvi bag with the, put them as far away from you body as you can.

If you want to be certain, find your local radiological protection officer and ask. He or She will be in the phone book.

With all risks it makes more sense to be aware of them than afraid of them. The consequences of falling into a crevasse are often fatal, but that means we take precautions like wearing crampons and roping up, not that we avoid glaciers altogether. It also makes sense to compare risks to other, similar risks we take without worrying in the slightest - hence my comment about radiation sources like granite houses and gaslamp mantles which we accept without question.

I actually believe that the various radioactive lenses are curiosities, not hazards. Pete's geiger reading does seem high, but note that even by today's safety standards, you are at the safe level for continuous exposure once you are six inches away. With a focal length of 7", you're fine even when focussing.

For what it's worth, I'm responsible for safety in a university research group that does a lot of X-ray spectroscopy, so I think I know what I'm talking about and can assess the risks for myself. I keep an Aero-Ektar in the house with my six-month old twins, but I don't store it under their bed - or mine.

However, I am reluctant to say 'forget it' , because there is so much confused and contradictory information about the Aero-Ektars floating about, and I want to do some real measurements before being certain. There are better and more convenient lenses which definitely have precisely zero risk of giving you cancer, so is even a small risk worth having that fast aperture around? The reason we take radiation seriously is that you have no sensation of being harmed until it is too late to do anything about it , which gives a certain incentive to educate yourself.

-- Struan Gray (struan.gray@sljus.lu.se), July 03, 2001.

Paul: If my Aero Ektar is typical, then as long as you don't bring the lenses in close contact with your body for any extended period of time (hours), then you really shouldn't worry.
Unfortunately, there's not much that will shield Gamma radiation completely. 2" of Lead or a foot or so of water will do the job, but distance is the cheapest way of protecting yourself.

I've just checked another old lens, a 14" f/9 Taylor-Hobson 'Cooke Apotal' process lens, which I suspect uses Lanthanum glass. This one drove the geiger counter to 300 counts/second, but the emission seems to be mainly high energy Beta and X-rays this time. It was the rear element again that appeared to be the source.
This lens was 'safe' at a radius of only 2 or 3 inches, and a 3mm sheet of Aluminium was enough to stop most of the particles.

A Kiev Mir-24N 35mm f/2 that I thought might be hot turned out to be completely clean.
I now have the use of a geiger counter for a day or two, and I'll be doing a sweep of my lens collection.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 03, 2001.

Pete, Struan, thanks for this most informative discussion! Seems we will never look at some lenses the same as before. As you say, there is probably not much to worry if simple precautions are taken. But we live in an environment that exposes us to cummulate small risks, radio-activity being just one of them with the remnants of Tchernobyl, but then there is the electro-magnetism and other bad rays from the computer screen, the diluted poisons in food additives, the mercury in tooth cement, the space and UV rays from the damaged ozon layer, the pollution in the air and water, the pesticides in the veggies and fruits, and for some, the white and deadly volutes of tobacco smoke just to name a few...

I better stop here this depressing list. The man of the future will have to be a transgenic creature blended with some cockroaches genes in order to survive, or will simply not be :-(

-- Paul Schilliger (pschilliger@smile.ch), July 03, 2001.

Heeee...heeee...eeeee...as someone who has had 9600 rads of radiation - I just wonder what you all think "safe" constitutes? The Dr.'s kept telling me it was good for me - although they all left the room prior to the linear accelerator being turned on. Sorry, Pete - just can't take this all that seriously - I just don't think most people have had enough radiation. Mutate or die...

-- steve (s.swinehart@worldnet.att.net), July 03, 2001.

Steve, if you drop an Aero Ektar in your lap, the tingling won't be subtle :-)

-- Struan Gray (struan.gray@sljus.lu.se), July 03, 2001.

200 counts of gamma a minute! Almost makes me think twice about flying in commercial aircraft (at least above 35,000 feet). Wait! No problem! I'll just book flights that last less than two hours (One per year in normal latitudes, or .2 per year over the South Pole).

Radon in the basement, on the other hand...

-- skip roessel (skiproessel@mindspring.com), July 03, 2001.

That was 200 counts per second, Skip. Only a factor of 60 difference!
I turned up two more hot lenses with the geiger counter. A Schneider 135mm f/9 Repro-Claron (Not the G-Claron), and a 55mm f/1.8 Pentax SMC Takumar. Both were low energy emission and not much to worry about.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 04, 2001.


Thanks for the info. I've been wondering what the proper method for affixing and Aero-Ektar to the cat was.

-- John H. Henderson (jhende03@harris.com), July 05, 2001.

Just take a look at what is being sold on Ebay. Those Rodenstock Heligon lenses come out of Xray machines, not process cameras.

-- Bob Salomon (bobsalomon@mindspring.com), July 05, 2001.

No worries John, just remember that it's kinder to shave the cat first.

-- Struan Gray (struan.gray@sljus.lu.se), July 06, 2001.


-- cxvxc (cxvcvx@ssds.kjjk), September 03, 2001.

-- cxvxc (cxvcvx@ssds.kjjk), September 03, 2001.

-- cxvxc (cxvcvx@ssds.kjjk), September 03, 2001.

Looks as this one has had a fair dose of Roentgen! ;-)

-- Paul Schilliger (pschilliger@smile.ch), September 03, 2001.

I trade WWII Aero lenses, all from the US Army Corps, 1940's, mainly Kodak, my favorite that I use with my Calumet is a 12"/5.0 Aero- Anastigmat, I also have a 12"/2.5 and a 13"/3.5, and a dozen Copying Ektanons and Copying Anastigmats, they don't glow green in the dark though, but I'm wondering if the risk is high enough to just toss them, or if there is no risk at all. I keep them all downstairs in the basement. Comments?

-- Jorge moreno (alf38@msn.com), January 14, 2002.


I just saw the thread, so I'm late. I do radiation protection for a living, and have for about 27 years now. The radiation protection field is based on the simple principle that no radiation exposure is acceptable without a corresponding benefit. Here, this means enjoying the benefits of a good lens.

The radiation levels associated with most lenses are relatively low compared to other consumer products and activities people perform. The human body has about 250,000 dpm of radioactivity, mostly from naturally occurring potassium-40. If you're worried about lenses, you should never, ever, consider flying since cosmic radiation levels go up as a function of altitude (10 mrem or so per flight, avg). Living in Denver for a year will expose you to many, many, times the yearly dose than being around most lenses. Oh, and get rid of those smoke detectors. Smoking adds 1-5 rem per year from radioactive lead which is a decay product of uranium and is concentrated by the plant. If you smoke, forget about lenses. The average dose per year is about 360 mrem, from nature in general. Fiestaware (the old orange stuff) was coated with uranium oxide and vaseline glass was also colored with uranium. So is dental porcelain (the uranium makes your dentures match your teeth under all types of light). Exposures from lenses would be miniscule compared to the sources above.

Thorium (and other rare earths like lanthanum) generally comes from monazite sand deposits, so don't worry about lenses if you live in Rio de Janerio, Kerala India, North Jacksonville Beach, or a large portion of the southeastern US coastal plains. The White Mountains in New England also have significant thorium so don't live there either. The southwestern US has a lot of uranium, so forget living there too. Not much left, is there?

The US Nuclear Regulatory Commission (and I assume the Brit's corresponding rulemongers) places restrictions on radiation levels from consumer products, and it used to be about 3-1/2 mrem per hour which would very roughly translate to 10,000 dpm with a geiger counter. The National Committee on Radiation Protection and Measurements (NCRP) has a publication on radioactive consumer products which is a nice read if you're interested. You should be able to find it in most good libraries.

Don't think old lenses are less radioactive. The daughter products are constantly replenished from the thorium parent, which has a half life of billions of years. However, if you want some real perspective, take your geiger counter through an antique shop and check the glass and glazed ceramics!!

-- Steve Hamley (sahamleyNOSPAM@netscape.net), March 20, 2002.

I too am late to this thread, but read its contents with great interest and amusement. As a radiologist, I am particularly impressed with the last response which is very informative. In all this discussion (some of it erudite), it is worth remembering that we bask in the life giving radiation of an enormous and self-perpetuating thermonuclear explosion i.e. the sun. As for 'no safe dose of radiation', without it we would'nt exist in the first place.I really would'nt worry too much about some old lenses.

-- Andrew Richards (drew.richards@virgin.net), March 25, 2002.

I *still* haven't made the measurements on my Aero Ektar, but Mikael Briggs has some worthwhile information here:

http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.ht ml

Mine now lives in the cellar rather than my camera cupboard. My wife wants me to get rid of it, but where else can I get a lens that burns bugs so spectacularly?

Incidentally, I read on usenet that at least some of the colour centers in some of the radioactive lenses can be bleached by leaving the elements exposed to sunlight. If you are using these lenses and want to get close to their original performance, this might be worth a try.

-- Struan Gray (struan.gray@sljus.lu.se), March 26, 2002.

Anyone tried these kind of tests on 35mm lenses? I have an FD 35/2 that's yellow and somwhere I read thorium was used in the glass, the lens construction is awesome, but I was concerned about the possible dangers, and if there's any possibility to get the originalk tint back. thanks

-- Max de Hertelendy (maxhert@bol.com.br), April 24, 2002.

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