Warning, radioactive lenses!

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'.<br>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.<p>I have a sample of a 7" Kodak Aero-Ektar, which is a lens that has a big reputation for being potentially radioactive.<br>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.<br>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.<br>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.<br>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!<br>I'll be testing the rest of my lenses as potential gamma sources as well in the near future.

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

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

the film?

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.

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.

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

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

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.

Pete,

 

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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,

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

in color?

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?

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.

 

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Dont't worry, be happy!

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!

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?

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.

 

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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.

 

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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.

 

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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.

 

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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.

 

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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 :-)

I'll try to answer as many points as I can.<p>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.<p>Geoffrey, I'll check again, but I'm sure

it was 200 counts/second.<p>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.<p>The Aero Ektar

used Thorium, not Lanthanum in the glass, and this is the reason why

this particular lens is such a 'hot' property.<br>I'll investigate

lenses containing Lanthanum, if

I can get hold of any, but I don't think they'll be as bad.<p>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.<p>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.<br>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!)<p>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?<p>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.<p>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.

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.

 

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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.

 

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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.

 

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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.

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?

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.

 

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If you want to be certain, find your local radiological protection

officer and ask. He or She will be in the phone book.

 

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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.

 

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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.

 

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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.

 

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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.

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.<br>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.<p>Update!<br>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.<br>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.<p>A Kiev Mir-24N 35mm f/2 that I thought might be hot

turned out to be completely clean.<br>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, 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...

 

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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 :-(

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, if you drop an Aero Ektar in your lap, the tingling won't be

subtle :-)

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).

 

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

That was 200 counts per <i>second</i>, Skip. Only a factor of 60

difference!<br>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.