Radioactive Repro-Claron

[thomas_vaehrmann]

Hi,

 

recently a message was posted here that Schneider Repro-Clarons might

be radioactive. As I owne one I gave it to a friend at a scientific

institute to run with a geiger-mueller over it. First thougt was that

there should be something wrong with the measurement because the

level seemed to be high. So the geiger-mueller was calibrated

according to their norm which is Co60 and a long time measurement

over three day started. Results: 305mm Repro-Claron serial# 9956938

from 1966 gave 15000 counts per minute (mainly gamma-rays), 135mm

Rodenstock Ysarex from the sixties gave 600 counts per minute,

background level was 40 counts per minute. It is the back lens of the

Repro-Claron that is hot, and it's color is yellow. The measurement

is absolutley serious and indicates that the used lens in the back is

not just contaminated with thorium but would consist app. 5% thorium.

Think about what you are using!

[donald_miller1]

Do you imagine that could be the cause of this serious and lingering cough that I have been having?

[c_p_goerz]

Thanks to extensive use with that lens I don't have to use X-Ray specs to see girls underwear! There are advantages my friend!

[michael_briggs2]

Two previous threads, "Warning, radioactive lenses!": http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0035DS and "355mm Repro-claron": http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004MVB, have reported measurements showing Repro-Clarons to be radioactive.

 

I have measured two Repro-Clarons. I am surprised that a measurement of three days duration was required: 15,000 counts vs a background of 40 counts per minute is easily measured in a few minutes with a Geiger detector. For the two that I measured, both the front and back are radioactive. This is easily verified by unscrewing the cells and measuring each separately. The radiation rate may seem a little less from the front because the mechanical construction won't permit a placing the glass as close to the detector. It is the outer elements that are radioactive. It would be strange if only the back were made with radioactive glass since Schneider described the lens as being of "completely symmetric construction" and that it is optimized for 1:1.

 

An original Schneider brochure that I have states that the lens is "designed as a four membered - four lens system on the Dialyt type (uncemented) principle" and that "new sorts of glass" are used. The "new sorts" of glass must be the thorium-containing glass, which was the first high-index of refraction, low-disperson glass developed. The Dialyt design is that used for the Artars, Apo-Ronars, and (later) Apo-Nikkors. It makes sense that it is the outer elements that are radioactive since these are the positive ones in the Dialyt design.

 

I have some information about thorium containing glass on my Aero-Ektar webpage: http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html. The Aero-Ektars were the first lenses to use thorium containing glass. I haven't had time to update my webpage with additional information. It seems that radioactive lenses are not rare -- most lens manufacturers used this glass at some time for some of their better lenses. The use was of thorium glass spread from Kodak after WWII and continued at least into the 1970s. The most famous LF lens with thorium glass is the Apo-Lanthar.

 

It was very common for manufacturers to emphasize the lanthanium content. This probably explains the origin of the false rumor that the radioactivity is due to contamination of the rare earths that were intentionally included in the glass. Many internet discussions of radioactive lenses contain additional false statements, so browse with caution.

 

Thorium containing glass should be suspected in any lens that appears to have a brown or tea color. This color is caused by self-induced radiation damage. It can be bleached away with UV light. I would be interested in hearing by email of other lenses that people guess to be radioactive from their color.

[pete_andrews]

At 15000 counts per minute, that Repro-Claron is about as 'hot' as my 7" f/2.5 Aero-Ektar, with its nice self-basting Thorium rear element.<p>Other hot lenses I've found have been a 12" Taylor, Taylor-Hobson Apotal process lens and a 50mm f/1.4 Pentax Takumar, but that's about it.<br>Surprisingly, a 14" TT-H Apotal of about the same vintage as the 12" version didn't raise a single count on the radiation detector.<p>BTW Michael: Thanks for the tip about UV clearing the brown discolouration of radiation damaged elements. I think I'll try to revive my Aero-Ektar.

[andrew_crump]

I have a tth 14" apotal which appears to have radiation damage,I was going to put it in a shutter--changed my mind now,amongst the usual takamars I also have a minolta 28mm mc lens which has a very yellow internal element

[michael_briggs2]

The 7 inch Aero-Ektar is larger than most Repro-Clarons and has two radioactive elements, but the externally measured radiation levels are more comparable than this would indicate because the thorium glass elements of the Aero-Etkar are internal elements, while the Repro-Claron thorium glass elements are the outside elements. On the Aero-Ektar, some shielding is being done by the barrel and the non-radioactive outside glass elements.

 

I bleached the brown from an Aero-Ektar with a 2 week long, 24 hour a day exposure with BLB fluorescent bulbs. Others have reported that sunlight will work.

[alpshiker]

Would the 305 G-Claron be in the same basket? I have one (SN 12 601 737) and I cannot notice any yellowing of the back element. But I have a Xenar 6.1/ 210 (S.N. 14 322 376), relatively modern lens, who has a developped a bold yellow tint in it's back element.

 

As far as my lenses are concerned, the champions are two older Asahi lenses for the Pentax 67 (105-150) which I had stopped to use because of their amber coloration. I will try to bleach them through UV exposure. Thanks for the tip!

 

Thomas, would you suggest that having these lenses, for instance in my bedroom cupboard, is hazardous for our health?

[david_du_busc]

I can't remember if it was Mick Jagger or Eugene Atget who suggested that if I wanted to appear more "manly" I should use a sock, not my 210 Apo Lanthar. Thanks for the hard facts.

[thomas_vaehrmann]

Hi again,

 

thank you all for your information. Just a remark to the measurment, the distance from lens to geiger-mueller was app. 8 inches. I'm no sepcialist on x-rays or doc but I've been told that others, especialy children, should stay away and I should use it with care. Perhaps someone else can give more precise rules of handling such lenses according to the dose the bring to us. Perhaps we should say goog-bye to them.

[pete_andrews]

Paul: The G-Claron doesn't contain any radioactive glass to the best of my knowledge.<p>David: It must have been Mick that gave you that piece of advice. Eugene would have known that you can't take decent pictures with an old sock!

[philip_glass]

Would a glass filter placed on the rear of the lens significantly attenuate the radiation emanating from the rear element?

[kelly_flanigan1]

Michael Re <i>"The 7 inch Aero-Ektar is larger than most Repro-Clarons and has two radioactive elements"</i><BR><BR>The 7 inch Aero Ektar of mine that is apart has two radioactive lens assemblies. This was verified by a counter. These are the two lens <b>asmeblies</b> behind the diaphram. The rear lens assembly is made up of two elements; one or both are radioactive; have not seen one with separated elements; both sides appear dark. The next lens assembly is also radioactive; it has a very deep radii negative surface by the diaphram. It appears to be two elements; but it is hard to tell.........I mention the point about assemblies because some internet info mentions that just the rear group is radioactives; which is wrong information. I have 3 of them; 1 for 4x5 speed graphic; and another for Exakta /Topcon 35mm; and a spare.<BR><BR>Do you have a cross section of the 7" Aero Ektar?<BR><BR>The 113mm F9 Printing Kodak Extar of mine is radioactive also; about the same as the 3 Aero Extars of mine. <BR><BR>My Coleman Lamps spare mantiles from the 1970's are equal in radioactivity as the lenses mentioned above. The new ones here sold are not.

[kelly_flanigan1]

Sorry about the spelling errors; the back button does not work here many times; and I have to get back to work.

[arne_croell]

An autoradiogram of Repro-Clarons is shown here:

 

http://www.photo.net/photodb/photo.tcl?photo_id=1221738

 

Right now I am "exposing" a 150mm Apo-Lanthar for an autoradiogram of that one.

 

Philip: A filter will not have a large effect, since they are usually made of a standard optical glass, maybe BK7, and are also thin. To have a pronounced absorption of the gamma rays, the glass would need to contain large amounts of heavy metal oxides, like lead oxide in a heavy flint glas (SF in Schott nomenclature). These are used in lenses, so a back element made from such a glass might reduce the gamma ray counts.

[eric_mims]

I heard Saddam's got an underground stash of 50,000 Repro-Clarons ready to unleash at any time.

[pvp]

There are/were a number of very fine lenses produced which contain thorium. Whether they are safe to use, or not, seems to be a choice left to the individual. FWIW, here's a link to a page that discusses the toxicology of thorium:<P>

<A HREF="http://www.atsdr.cdc.gov/tfacts147.html">http://www.atsdr.cdc.gov/tfacts147.html</A>

[mike_rosenberg1]

I found this to be an interesting thread. The example of exposure of T100 film is especially illuminating. Has anyone thought about what these lenses are doing to film while in a backpack? I would be careful on long trips! But here is another thought - this exposure would be worse with some other films.

 

Another thought - will these lenses be detected in the newer airport security measures? Better have your local physcists write you a note...

 

Mike

[michael_briggs2]

<p>

My terminology in my description of the Aero-Ektar uses "assemblies", "groups" and "elements". This description applies to the very common 7 inch f2.5 Aero-Ektar; some other Aero-Ektars have different designs. Usually these

lenses unscrew into three pieces, a front assembly containing glass, a middle part without glass, and a rear assembly with glass. With a Geiger counter will quickly find that the front and middle assemblies are not radioactive, while the rear assembly is. This is what I mean when I say that rear assembly is the radioactive portion of the Aero-Ektar.

</p>

 

<p>

If one disassembles the rear assembly, one will find two pieces of glass, and if one looks at the sides of the pieces, one will see that each piece has been formed from two smaller pieces. The standard terms for these in optics are "group" for the cemented-together piece and "element" for the individual pieces that were cemented together to make the groups. With a Geiger counter, one will find that both groups from the rear assembly

are radioactive. Also, for both groups, the radiation is higher from one side. This shows that each group from the rear assembly has one radioactive element.

</p>

 

<p>

A diagram of the 7 inch and 12 inch f2.5 Aero-Ektars of WWII is appears as Figure 8.7 of "A History of the Photographic Lens" by Rudolf Kingslake and also in US Patent 2,343,627 (<a

href="http://patft.uspto.gov/netahtml/srchnum.htm"> available online from the patent office search page</a>). In these diagrams, the front of the lens is to the left. The lens is seen to consist of 7 elements in 4 groups. The patent numbers the elements from I to VII, left to right. The radioactive elements are elements V and VI, of the third and fourth groups. Besides the measurements that I have described, this identification can also be made by correlating the

optical properties of the glasses, as listed in the patent, with the published optical properties of Kodak's thorium containing glass.

</p>

 

<p>

A hope that this makes the statement on <a href="http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html">

my Aero-Ektar webpage</a> "For the f2.5 models, the rear optical assembly consists of four lens elements cemented into two groups: the radioactive lens elements are the two inner elements.", completely clear.

</p>

 

<p>

Returning to the original question, Figure 6.18 of Kingslake's books shows the cross-section of the Goerz Celor, which is the dialyte design used for the Repro-Claron, consisting of 4 elements in 4 groups. The thorium containing elements of the Repro-Claron are the two outer elements.

</p>

 

<p>

As to Philip's question about whether a glass filter would block the radiation, I agree with Arne that the bulk of the gamma-rays would pass through the filter. However, thorium and its radioactive daughter isotopes emit several types of radiation including x-rays of lower energy than the gamma-rays. Some of these radiations will be attenuated by a glass filter.

</p>

 

<p>

As to Mike's question about the effect on film, this is something to be concerned about for long-term storage of a lens containing thorium glass in close proximity to film. An auto-radiogram made through the plastic darkslide of a filmholder, with the lens touching the darkslide, causes significant density on Delta 400 in 12 days. Moving the lens even 6 inches from the film will greatly decrease the exposure. At this distance I don't think that film would be effected at a level of photographic significance in a few days.

</p>

 

<p>

The toxicology fact sheet located by Alan is interesting, but doesn't seem to me to be relevant to evaluating the hazard of thorium containing glass. The fact sheet reports the effects of breathing thorium dust (or of injecting! thorium into the body). I don't think any of us plan to grind our lenses into dust — this would be hazardous and is illegal in the USA. I agree with Alan that each individual will have to decide whether the lenses are safe enough

to use.

</p>

 

<p>

I made a few comments about the dangers of thorium containing glass <a

href="http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html"> on my webpage</a>. My opinion is that the danger is small if one doesn't store the lens in close proximity to a human, but I still haven't had time to do careful calculations and comparisons. There are many other decisions that cause increases in radiation exposure that people commonly make without considering the radiation: living in areas with higher levels of uranium or thorium in the ground, living at higher altitudes or flying, especially flying at higher latitudes, and smoking cigarettes.

</p>

[kelly_flanigan1]

Michael; my comments about the elements and groups was not directed towards you website or you. I meant to say that others have impiled that only the last two elements making up the last group are radioactive. Many state that two elements are radioactive; but dont mention the group. <BR><BR>Elements number V and VI are radioactive; of groups 3 and 4. Radius 9 of element VI on my 178mm F2.5 Ektars is very shallow negative radii; like patent 2343627 shows in Figure 1. My American Optical lens measure reads this surface as -0.75 diopter.<BR><BR> <b>Kodak optical glass with a Nd above 1.70 ; from patent info:</b><BR><BR>

 

<BR><BR>** Note: Nd=1.720 V=29.3 in patents is close to Shott SF-1; with Nd=1.71736; V=29.51

<BR><BR> Other three glasses are nearest neighbors to Schott N-LAF-2; with Nd= 1.74397; V=44.85<BR><BR>

 

 

<BR>patent 2343627 AKLIN /Kodak 7 elements in 4 groups 100mm F2.5

<BR>element in groups sequence = 1/2/2/2

 

<BR>element #V Nd= 1.745 V=46.4

<BR>element #VI Nd= 1.755 V=47.2

 

<BR><BR><BR>patent 2289779 HERZBERGER/Kodak 8 elements in 4 groups 100mm F1.5

<BR> element in groups sequence = 1/2/2/3

 

<BR> element #V Nd=1.744 V= 45.8

<BR> element #VI Nd=1.744 V=45.8

 

<BR><BR><BR>patent 2262998 FREDERICK &HERZBERGER/Kodak

<BR> 7 elements in 4 groups 100mm F1.4

<BR> element in groups sequence = 1/2/2/2

 

<BR>element #VI Nd=1.744 V=45.8

(2nd scheme)

 

<BR><BR><bR>patent 2252682 AKLIN/Kodak 7 elements in 4 groups 100mm F1.5

<BR> element in groups sequence = 1/2/3/1

 

<BR>element #V Nd=1.720 V=29.3 ***

(1st scheme)

 

<BR>element #V Nd= 1.720 V=29.3 ***

<BR><BR>element #VI Nd= 1.744 V=45.8

(2nd scheme)

 

<BR><BR>element #V Nd=1.720 V=29.3 ***

(3rd scheme)

 

<BR><BR><BR>patent 2252681 AKLIN/Kodak 7 elements in 4 groups 100mm F1.9

element in groups sequence = 1/2/2/2

 

<BR><BR>element #V Nd=1.744 V=45.8

<BR><BR>element #VII Nd=1.744 V=45.8<BR><BR><img src="http://www.photo.net/photodb/image-display?photo_id=1338110&size=lg">

[kelly_flanigan1]

<img src="http://www.photo.net/photodb/image-display?photo_id=1338184&size=lg">