Canon Lens FD 35mm 1:2 S.S.C. and low-level radioactive hazard

[john_ratliff1]

Have you wondered about the potential radioactive hazard for the Canon 35mm F-2.0 SSC lens with the

radioactive thorium-fluorite element? Well, let me answer this after a few lines of introduction to a

problem I had recently.

 

I am an industrial hygienist, who was tasked with the job of providing some training to our customer

engineers for a high tech firm where we had a machine which emmitted X-rays. We needed to train

them in the use of our new ionizing radiation detectors, one a scintillator and one a Gieger counter (see

http://en.wikipedia.org/wiki/X-ray for details). But I did not have a source of ionizing radiation to

use. I tried to use a lantern mantle, but they have gone away from the radioactive types. I tried other

sources, like table salt (which has low levels of radioactive potassium iodide in it), but that did not work

either. Finally, I found my source.

 

The source was the Canon 35mm F-2.0 lens mentioned above. This lens contains a radioactive thorium

floride lens element in it. Here is what Wikipedia and others say about the lens.

 

"Added to glass, it helps create glasses of a high refractive index and with low dispersion.

Consequently, they find application in high-quality lenses for cameras and scientific instruments..."

http://en.wikipedia.org/wiki/Thorium

 

"Note: incorporates radioactive, thorium floride ("rare earth") glass which imparts a warm green tinge to

the pictures. Best use as an exceptional quality lens for black and white photography, since it doesn't

match the color of other Canon FD lenses and will color cast color slides. Very high contrast at all but f/

5.6 and f/8 where it is extremely high. Optimum aperture f/5.6." See the below link for the lens (scroll

down), as it has the ratings at various stops as well as the other information quoted above.

http://members.aol.com/canonfdlenstests/default.htm

 

I have now used the lens in several training sessions. We need to train our engineers to be able to

detect faint X-ray leaks on our machines. We use the level of 0.6 microSieverts an hour (0.6 uSv/hr) as

our cutoff, which is very low. We do this, even though the average person traveling on a passenger jet

will receive more than this amount, because of the principle known as ALARA. ALARA means that there

is no amount of radiation that is "safe," and that even though the body has mechanisms for coping with

radiation damage, we don't ever know that that damage will lead to cell mutation from DNA damage.

ALARA means "as low as reasonably achievable."

 

See; http://en.wikipedia.org/wiki/Sievert

for more information about measuring radiation in microSieverts.

 

We first survey with a scintillation detector, as it will detect the low levels in a rate-count mode (counts

of ionizations per second) that is very low. It alarms at 75 counts per second. I had several items

scattered on a desk, and asked a engineer to survey those items, as one was a radiation source. The

alarm sounded at 87 decibels when the engineer moved the detector over the lens, about half an inch

from the lens, and she jumped back surprised. The counts per second reading went to about 150 cps.

We then took the Gieger counter and got an accurate reading of the actual radiation. It read between 1

and 2 microSieverts per hour (1-2 uSv/hr), settling at 1.5 uSv/hr for a time. At the eye cup, the reading

was about 1 uSv/hr.

 

What does this mean to us as photographers? Well, I was carrying that lens around all week, and took a

lot of photos with it. Because I was using it as a prop, I wanted to have it there all week. I got a camera

pass, and it turns out I had the only camera pass at the safety workshop. But I took care not keep the

lens to my eye for any period longer than necessary to focus and take the photo. I also walked a lot (I

decided to walk rather than use a rental car for the week), and had the camera strapped over my

shoulder. I normally rest my lower arm over the camera and lens, but decided not to with this one. The

Wikipedia link above states that this is alpha radiation, but it is not stopped by paper (which I confirmed

with the Gieger counter). I therefore think that at least some of the radiation is beta radiation, which

can go out a bit further. The radiation drops off very quickly, and is not readable about four inches

away from the lens. But if you think about it, every second that my eye is at the camera to take the

photo, I'm receiving about 150 ionizations. These add up in a hurry. I have therefore discontinued

using this lens for all but the radiation survey courses.

 

Why? ALARA--I want my exposures to radiation kept to a minimum, and if I have no need for that

exact lens, I will have no further exposures. In the scheme of things, this exposure is pretty minor, but

if it is preventable, then I will prevent it. One of the effects of ionizing radiation is an increase in

catarachs, and this is something I would like to avoid too. It must be emphasized that this is not

whole-body dosing, but very limited to a small part of an arm, and the face. But all ionizing radiation

interactions will have an effect, and I wish to minimize them on myself. What does this mean to

photographers? I don't know, as everyone will have to make up their own minds. But at least you have

some information to go on. The lens is a very good one, and I've enclosed some photos to show its

capabilities.

 

John

 

PS--I posted an earlier story associated with this trip, which was removed. If I offended anyone with

that story, my apologies. I was simply trying to describe the evening as it happened.<div></div>

[pvp]

John,

 

Thanks for the excellent discussion on the realities of radioactive lenses.

 

As for the radiation, while Thorium 232 is itself an alpha emitter, several of the daughter elements are beta emitters and at least one daughter element emits a high energy gamma ray when it decays (1.2MEV, if memory serves.) With a 15,000 year half-life, Thorium doesn't go away quickly, and with beta and gamma emitters in its decay series, a lens containing Thorium will actually be more radioactive now than when it was manufactured.

[john_ratliff1]

The above photo was made with Fuji ISO 50 Velvia slide film. Here is another, of a building

which is reflecting an image.<div></div>

[john_ratliff1]

Another photo with this FD 35mm, F-2.0 Lens, taken on one of my walks. It is of a fountain

on the Great American Expressway.<div></div>

[john_ratliff1]

A final exposure of the statue of Our Lady of Peace, taken after sunset.<div></div>

[User_502260]

There have been many threads here on radioactive lnses in general and the 35/2 FD SSC with the concave front element in particular. I have one of these and it is indeed a very good lens. It is now sitting in front of a desk lamp with a CFL bulb shining through it and with aluminum foil at the back end. I hope there is enough UV light coming from the CFL bulb to do the job. Over some undetermined period of time I hope to get the yellowish cast to disappear. While this is happening I am shooting with a newer 35/2 New FD which is also a very fine lens. I realize that the "bleaching" of the color cast from the SSC lens will not have any effect on its radioactoivity.

 

In the time I have had this lens I have not noticed any fogging of film. If the lens is not stored for a long period very near to your body then the question is how much radiation reaches your eye with the lens mounted on a camera body. I would typically use this lens on an F-1 or an EF body. Does a camera body with more metal like an F-1 or an EF provide ay better shielding for your eye than a body with more plastic like an AE-1? I have read that it has not been legal for many years to have an eyepiece made of glass containing thorium.

 

At some point I would like to add a later 35/2 FD SSC with the convex front element just to round things out and see how good it is.

[gnashings]

That's a great story and the input of someone highly qualfied to comment on this subject is very much welcome after the usual 3rd hand advice that people pass on (usually with the best of intentions, of course). And I think that in a world as riddled with a variety of unseen hazards, its probably a good idea to remove any sources of harmful radiation, even if it is small - or at least that is what my understanding of the ALARA principle is. Thanks for a valuable bit of insight.

[luis triguez]

There were similar posts in the pass in Leica forum about the soviet Industar 61 L/D (55 mm). I have one of those and seldom use it but I have to recognise it is a great razor lens.

[frederick_muller]

I've got the Canon 35mm f2 Concave and the 35mm f1.4 Nikkor. Both have radioactive Thorium, both cleared up with exposure to direct sunlight ... the Nikkor was badly yellowed and cleared with 40 hours total sunlight exposure.

 

I'm curious as to just how material the hazard is here. I mean, compared to getting a chest x-ray at the hospital, or getting dental x-rays, just how big is the dose from carrying one of these lenses around as part of your kit for a year?

[w_t1]

Is the moral of the story don't put that baby on your lap? Interesting the timing of things....cell phones are hazardous, then it was laptops on the lap, now we're talking aobut lenses made when I was in junior hs thank God AG invented the net. I think you should send this info to the PSA people in boulder that have ads about dangers of air turbulence. Did you know the body isn't made to handle air turbulence, but it is made to handle skateboarding? In all seriousness, I'd be interested in reading the earlier story of yours that was removed - send to my email if you can. You can never tell around here (this forum) what is kosher and what is not. Tom

[danielleetaylor]

Let me get this straight: you're talking about 2 uSv per hour if you hold the thing to your body, right?

 

Average natural background exposure is 2,400 uSv per year. Medical doses can run 1,000 uSv per year. And in some locations, the natural dose is far, far higher. (Don't think that must be "somewhere else". You may live smack in the middle of a high natural dose region.)

 

Unless you sleep with that lens, I don't think I would worry about it. "No safe exposure" sounds good as public policy but is not supported by observation. If it were true life would not have made it this far. If "no safe exposure" is the rule then you should buy burkas for your family to eliminate UV exposure first, then worry about the lens, because UV is far more deadly due to far higher and more constant daily doses.

 

To say nothing of non-radiation risks. The risk posed by that lens, used 40 hours a week for a decade, has got to be lower than the risk of driving to work daily. Look up car death statistics and consider what "no safe exposure" means in that context.

[pvp]

Apples and oranges. You (I hope) drive carefully because that is how you can minimize your exposure to the risks inherent in motor vehicle travel. You probably use a sunscreen, at least some of the time, to reduce your exposure to UV and its hazards. Denying that radiation poses a health hazard is, frankly, just a way to rationalize your choice to take an avoidable risk.

 

High energy gamma rays are known to cause chromosomal damage and cancers. Nobody can say how many of those gamma rays will pass harmlessly though your body, but it may only take one to put you in a box. The principle behind ALARA is to minimize your exposure, so as to reduce the chance of being in the way of "the one." If you happen to absorb the one that causes a cancer, you won't like it; trust me.

 

Personally, I don't feel my quality of life is lessened by not using radioactive lenses, nor do I see an adverse impact on my photography. As before, YMMV...

[john_ratliff1]

Jeff, I'm going to take my F-1N to work tomorrow, when we have an instrument dealer coming over, and take some more readings to see what I get.

 

Frederick wants some comparisons, and Daniel gave a few. But Daniel compared two separate risks (driving with ionizing radiation) that do not include the radiation. This is still somewhat valid for looking at overall death rates, etc., but not for tissue risks. I did take a radiological health course from Tulane University's Center for Applied Environmental Public Health (CAEP) last winter (I'm studying for a Master's Degree in Public Health--Industrial Hygiene) and received these comparisons in a slide:

 

Natural background and manmade radiation

(annual average dose equivalent, including radon): 360 mrem Diagnostic chest x-ray: 10 mrem

Flight from LA to Paris: 4.8 mrem

Barium enema: 800 mrem

Smoking 1.5 packs per day - 1 year dose: 16,000 mrem

Heart catheterization: 45,000 mrad

Mild Acute Radiation Sickness*: 200,000 mrad

LD50 for Irradiation*: 450,000 mrad

 

(mrem = millirem = 1/1000 rem; 0.6 uSv/hr = 0.06 mrem/hr; 1 Sv = 100 rem)

 

Annual Regulatory Limits:

 

Members of the public: 100 mrem

Occupational limits:

Total effective dose equivalent: 5 rem

Lens of the eye: 15 rem

Single organ dose equivalent: 50 rem

Skin dose equivalent: 50 rem

Extremity dose equivalent: 50 rem

 

5 rem = 0.05 Sv = 50 mSv

 

So lets say the lens of the eye receives 1.5 uSv/hr from the Canon lens. Since 1.5 uSv/hr equals 0.15 mrem/hr, that would be 0.15 mrem/hour, and the dose limit is 15 rem per year. To get a year's dose, you would need:

 

0.15 mrem/hr x 1000 mrem/rem x 15 rem/dose limit = 2250 hours on the lens to get the year's dose limit of ionizing radiation from this lens.

 

This sounds like a lot, but remember that ionizing radiation is not the only cause of cataracts. So is non-ionizing radiation, like sunlight. There are be cumulative effects, as airline pilots have a higher rate of cataracts than do the rest of the population, and that is thought to be because of ionizing radiation from space, which doesn't have the atmosphere to blunt it.

 

This gets us back to the ALARA concepts above. ALARA is defined as:

 

"ALARA (?As Low As Reasonably Achievable?) means making every reasonable effort to maintain exposures to ionizing radiation as far below the regulatory dose limits as practical, taking into account economic, societal, and other relevant considerations." (Dr. Ronald Goans, Tulane University Center for Applied Environmental Public Health)

 

Here is how to minimize exposures to external ionizing radiation:

 

--Minimize the time spent near the radiation source

--Maximize the distance away from the source

--Make use of available shielding

--Minimize the quantity of radioactive materials handled

 

As stated in my first post, this is a minimal hazard for ionizing radiation, which is why I felt comfortable carrying and using the Canon FD 35mm, F-2.0 lens above. But that also means that I will not be using it regularly, or even occasionally. I'll use it only when I feel an acute need, and realize that I am absorbing some radiation dose when I do.

 

John

[frederick_muller]

Thanks for the detailed figures John. This is the first time I've seen the risk from these lenses actually quantified on this forum, and it is appreciated.

 

It sounds to me that if one carries this lens in a gadget bag, 4 inches from direct contact, it's safe. If one takes it from the bag, mounts it, works with it casually three hours a week, he'll get 3*52*.15 = 23.4 mrem per year. But that's 156 hours per year of direct contact, with the lens mounted, in one's hands, or raised to the eye. On its face, occasional use looks pretty safe. If it sits on a shelf in the living room, or in a gadget bag in the closet, it's pretty safe too.

 

I agree with you ... the figures impress me enough that I am not going to be fondling these lenses when they are not in serious use.

[john_ratliff1]

Jeff,

 

I took the lens on my Canon F-1N, with a power winder and an AE Finder FN mounted on it

the body. I met with a representative of ThermoFisher, who makes the Mini900 GM

counter that I use. I wanted to show him the ionizing radiation source that I was using in

the training. In the process, I was able to get measurements of the radiation at the eye

cup of the AE Finder FN with the 35mm F-2.0 lens. Here are the measurements from

today:

 

--At 1/4 inch off the lens focus ring, 1-2 uSv/hr, settling to about 1.5 uSv/hr over time

(as reported above).

--At the eye cup, where the eye would be, 1 uSv/hr (it settled there, and varief from about

0.6 to somewhat over 1.0 uSv/hr).

 

Again, these are not high, but are above where my company measures for a radiation leak

on our machines (0.6 uSv/hr).

 

For the sake of clarity, I will repost the typical radiation from above. I am doing that

because above it did not come out in tabular format, and is therefore hard to see. Here is

what it should have looked like:

 

Natural background and manmade radiation (annual average dose equivalent, including

radon): 360 mrem

 

Diagnostic chest x-ray: 10 mrem

 

Flight from LA to Paris: 4.8 mrem

 

Barium enema: 800 mrem

 

Smoking 1.5 packs per day - 1 year dose: 16,000 mrem

 

Heart catheterization: 45,000 mrad

 

Mild Acute Radiation Sickness*: 200,000 mrad

 

LD50 for Irradiation*: 450,000 mrad

 

Note, these have two units, mrad and mrem. The "m" stands for "milli," and is 1/1000.

"Rad" is "radiation absorbed dose," and "rem" is "radiation equivalent in man," which uses a

multiplier for the type of radiation, as different types have different effects on biological

systems (alpha verses beta verses gamma verses x-rays, for instance). Also note the dose

a smoker is receiving.

 

I also gave annual regulatory limits (USA--other countries may be lower in some cases,

higher or non-existant in others):

 

Members of the public: 100 mrem

 

Occupational limits:

 

Total effective dose equivalent: 5 rem

 

Lens of the eye: 15 rem

 

Single organ dose equivalent: 50 rem

 

Skin dose equivalent: 50 rem

 

Extremity dose equivalent: 50 rem

 

 

Hopefully, this will come out easier to read.

 

John

[john_r7]

Hello all,

I have been following this discussion with great intetest. Seems it's pretty risk free for us occational hobby-photographers to use this lens, don't you agree.

 

Is this is the only Canon FD lens having this Thorium treatment? There are other Fluorite lensses, for example the 300mm and 500 FL-F?

 

John R

[frederick_muller]

I knew smoking was dangerous, but the smoking figure of 16,000 mrem blows me away. What's radioactive in cigarettes?

[john_ratliff1]

According to a quick Google search, the radioactive elements in cigarette smoke are:

 

--Polonium-210 (Po-210)

 

--Lead-210 (Pb-210)

 

--Radium-226 (Rd-226)

 

Radium-226 decays into radon, and Po-210 and Pb-210 are "long-lived decay products of

radon. Sticky hairlike structures on both sides of tobacco leaves collect these from the

atmosphere. Tabacco roots also absorb some radioactivity from the soil." K.S.

Parthasarathy, Secretary, AERB, source:

http://www.hindu.com/thehindu/seta/2003/06/05/stories/2003060500020200.htm

 

According to this internet source, Carol W. LaGrasse, P.E., member Adirondack Branch

Advisory Council of the American Lung Association of N.Y. State, 1986, "For a person

smoking 1 1/2 packs of cigarettes a day, the annual radiation dose to the surface of

bronchial cells at bifurcations is the equivalent dose to the skin from taking 300 chest X-

rays per year." Here's that source:

 

http://prfamerica.org/RadioactivityInCigaretteSmoke.html

 

I'm concerned here as my Mother died of lung cancer and emphasema from cigarette

smoking. I am currently taking a course in Epidemiology from Tulane University Center for

Applied Environmental Public Health, and read the first chapter of my text today. In it, Dr.

Leon Gordis ("Epidemiology, Third Edition) states:

 

"Consider cigarette smoking and lung cancer. We do not know what specific component in

cigarettes causes cancer, but we do know that 75% to 80% of cases of lung cancer are

caused by smoking...Since 1987, more women have died each year from lung cancer than

from breast cancer. Thus, we are faced with the tragic picture of a preventable form of

cancer, lung cancer, which results from a personal habit, smoking, as the current leading

cause of death in American women.

 

"Furthermore, in 1993, environmental tomacco smoke (secondhand smoke from other

people's smoking) was classified as a known human carcinogen by the Environmental

Protection Agency, which attributed about 3,000 lung cancer deaths in nonsmoking

individuals each year to environmental tobacco smoke.

 

"Although rates of smoking in those older than 189 years of age appear to have decreased

in recent years in the united States, a troublesome observation is that, from 1991 to 1997,

the prevalence of smoking in high school students increased 32%. Thus, the scourge of

smoking remains one of the major unmet prevention challenges for practitioners inbo th

public health and clinical medicine." (page 13)

 

The difference between the lens exposure and cigarette smoke is three-fold:

 

--Cigarette smoke is an internal hazard, whereas the lens has radiation outside the body.

 

--Cigarette smoke's radiation is in direct contact with interior lung tissues and cells,

whereas the lens is outside the body, and the distance is much greater.

 

--Cigarette smoke's radiation is mostly alpha radiation, which is not really dangerous until

it gets inside the body, and then it is deadly. Alpha particles are huge compared to other

particles, and whereas it does not penetrate deeply, what it hit it really wacks hard. In

converting rads (radiation absorbed dose) to rems (radiation equivalent in Man), a quality

factor is assigned to various types of radiation. For X-rays, beta radiation, and gamma

radiation, that factor is "1". For alpha radiation, depending upon the energy level, that Q-

Factor is 1-20. If the alpha-emitter is 20, and it is next to the tissue, the tissue is

absorbing 20 times the damage from that radiation than if than radiation was an X-ray.

 

So if your choice is between using the Canon FD F2.0 lens with the thorium-floride

element, and qutting smoking, by all means enjoy the lens and quit smoking.

 

John

[john_ratliff1]

That should have been "18 years of age" in the quote above. 'Sorry about that.

 

John

[alex_kinnan]

"That should have been "18 years of age" in the quote above. 'Sorry about that. "

 

I should say so! If one had the body of a late-adolescent at 189 years of age, then I would imagine that cigarettes wouldn't be getting such a bum rap.

 

Seriously though, I've long been fascinated by this subject and have found this an interesting thread. If you've run any similar tests on old Pentax lenses, I would be most interested in reading the results...