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Radioactive lens design
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PostPosted: Mon May 29, 2017 10:29 pm    Post subject: Radioactive lens design Reply with quote
Hi everyone, I was thinking about radioactive lenses recently and got a question that you might be able to answer. Lenses like the Fujinon 50/1.4, Rokkor 58/1.2, Pancolar 50/1.8, etc. were designed to use lens elements doped with thorium. As many here know that changes the optical properties of the glass. And from what I understand the lenses I listed and probably some more exists in both radioactive and non radioactive versions, while keeping the same layout. So when they removed the thorium, they had to replace it with other metals right? Or did they just remove it and it works fine anyway?

And while we're at it, how common was the use of lanthanum and other non radioactive elements in MF lenses?


PostPosted: Tue May 30, 2017 5:47 am    Post subject: Reply with quote
The lens layout you see in manuals or such are likely with "some" tolerances. So I would not take them as an exact reference.
So the R&D department has to change the lens design for the new enviromental / user safety requirements by law. When they are ready they go with the result to product managament, and tell the lens layout on the packange and manual has to be changed one miilimeter here and one millimeter there. This adds additional cost for no real benefit.

Normaly a replacement of a glass with a different glass can result in quite a lot of work for the lens designer. He could try to keep for example the mecahnical parts about the same, or even some of the lenses he has not to change. But from my point of view it is unlikely that he only relaces the glass type and everything is fine. Perhaps in a lens with low quality demands this is possible, but I don´t think this is the case on fast double gauss lenses for photography.


PostPosted: Tue May 30, 2017 3:10 pm    Post subject: Reply with quote
Think of a lens design like a math equation, when you change a variable, you effect the balance of the equation, so to balance it again you must recalculate other variables to bring it back into balance.
So if you change the refractive index of an element, the shape of the element(and others) will have to be altered to rebalance the lens formula so you can get a sharp image.
Lead and radioactive doping has been banned so as to remove the danger to the workers that grind the lenses, not so much to protect the consumer who buys and uses the finished product.


PostPosted: Tue May 30, 2017 3:53 pm    Post subject: Reply with quote
It would be interesting to know much redesigning that had to be done. I have yet to acquire a pair of an original and recalculated lens for practical testing. Only for the sake of curiosity of course.

http://camerapedia.wikia.com/wiki/Radioactive_lenses

On this Camerapedia page they wrote this.
Quote:
Thorium oxide has a crystalline structural similar to calcium fluoride (fluorite). Like fluorite, its optical properties of high refractivity and low dispersion allows lens designers to minimize chromatic aberration and utilize lenses of lower curvature, which are less expensive to produce.


So the main reason to use thorium oxide to keep the price down? Does anyone know if the prices went up when they re-released recalculated versions?


PostPosted: Tue May 30, 2017 4:28 pm    Post subject: Reply with quote
blotafton wrote:
It would be interesting to know much redesigning that had to be done. I have yet to acquire a pair of an original and recalculated lens for practical testing. Only for the sake of curiosity of course.

http://camerapedia.wikia.com/wiki/Radioactive_lenses

On this Camerapedia page they wrote this.
Quote:
Thorium oxide has a crystalline structural similar to calcium fluoride (fluorite). Like fluorite, its optical properties of high refractivity and low dispersion allows lens designers to minimize chromatic aberration and utilize lenses of lower curvature, which are less expensive to produce.


So the main reason to use thorium oxide to keep the price down? Does anyone know if the prices went up when they re-released recalculated versions?


Yes, why not keep the price down if they can? Other materials were added to increase performance and reduce aberrations, something that may not necessarily be fixed by the curvature alone - chromatic aberrations. You would have to check photography magazine pricelists or any other contemporary sources to confirm something about the price, but generally I think the price of camera equipment has always largely been going down. One interesting example I came across was that the Minolta MD 85/2 which replaced the MC-X 85/1.7 actually cost more - yes it had increased performance but it was also dimmer. It must have been a tricky sell at the time... But we cannot say whether the price increase is due to an increase in material costs, or value-added performance, or financial troubles of the company, or a slow photographic market etc.

Only the largest companies had the freedom to do their own research and development on new glass compositions, and compute the designs before they were prototyped, and get the best, unique product to the market sooner. Companies which didn't have these capabilities themselves would just put a request to industry to find a market solution. Of course, the materials used and available for glass all across the world are not the same and what's available changes over time.

When the Soviets took the Zeiss employees and equipment, the lenses were supposed to be produced exactly the same, because they used OEM equipment, operators and the raw materials from Germany. Eventually, they had to recalculate the glass to be produced from materials available in the USSR, but I suppose they aimed to largely keep the design the same so they could continue to use the existing equipment/process without trouble. The easiest things to improve were the coatings.


PostPosted: Tue May 30, 2017 4:38 pm    Post subject: Reply with quote
As others have said, when you change the glass, you have to change the lens formula somewhat. Thorium glass has high refractive index and low dispersion. If you change the refraction index, you have to recalculate the lens completely. Low dispersion glass reduces CA, which means that you can use simpler lens design (you need aspherical elements or extra corrective elements to achieve the same effect with normal glass). So thorium lenses were a way to get good optics on the cheap.


PostPosted: Tue May 30, 2017 5:47 pm    Post subject: Reply with quote
Good answers, thanks!

This is me when taking pictures Wink



PostPosted: Thu Jun 01, 2017 4:25 am    Post subject: Reply with quote
fermy wrote:
As others have said, when you change the glass, you have to change the lens formula somewhat. Thorium glass has high refractive index and low dispersion. If you change the refraction index, you have to recalculate the lens completely. Low dispersion glass reduces CA, which means that you can use simpler lens design (you need aspherical elements or extra corrective elements to achieve the same effect with normal glass). So thorium lenses were a way to get good optics on the cheap.


It wasn't a price thing. They couldn't make fluorite crystals in the sizes needed for some of these lenses. Crown glass with thorium was easy. Until Canon and Takahashi (telescope maker) started using fluorite in their products in large sizes. Even so, at $600/lb, making a 10" wide, 15lb fluorite element for a Kodak Aero Ektar aerial surveillance lens would have been pricier than thorium which is cheap. Also, all good lenses need to be recomputed for each glass batch as they vary in characteristic.


PostPosted: Thu Jun 01, 2017 6:41 am    Post subject: Reply with quote
RichA wrote:
...Also, all good lenses need to be recomputed for each glass batch as they vary in characteristic.


Melt fitting is only made for few high end lenses, from what I learned in lens design workshops and books (for example "Lens Design" by Laikin).


PostPosted: Thu Jun 01, 2017 9:29 pm    Post subject: Reply with quote
RichA wrote:

It wasn't a price thing. They couldn't make fluorite crystals in the sizes needed for some of these lenses. Crown glass with thorium was easy. Until Canon and Takahashi (telescope maker) started using fluorite in their products in large sizes. Even so, at $600/lb, making a 10" wide, 15lb fluorite element for a Kodak Aero Ektar aerial surveillance lens would have been pricier than thorium which is cheap. Also, all good lenses need to be recomputed for each glass batch as they vary in characteristic.


Sure, price was not the only consideration. For instance, before the use of computers became practical in the field, calculating an extra corrective element was very difficult, sometimes prohibitively so. However, approximately from the end of 1950s the use of thorium in consumer lenses was primarily to save costs.


PostPosted: Thu Jun 01, 2017 10:23 pm    Post subject: Reply with quote
RichA wrote:
Even so, at $600/lb, making a 10" wide, 15lb fluorite element for a Kodak Aero Ektar aerial surveillance lens would have been pricier than thorium which is cheap.


Where did you find that price?
Just curious, I had no idea about fluorite price. I assume lab grown fluorite.


PostPosted: Sat Jun 03, 2017 5:55 am    Post subject: Reply with quote
Himself wrote:
RichA wrote:
Even so, at $600/lb, making a 10" wide, 15lb fluorite element for a Kodak Aero Ektar aerial surveillance lens would have been pricier than thorium which is cheap.


Where did you find that price?
Just curious, I had no idea about fluorite price. I assume lab grown fluorite.


That came from a manufacturer of high-end telescopes. Six-sigma fluoro-crown glass ("ED glass") is about the same price, but few use it.


PostPosted: Sat Jun 03, 2017 5:58 am    Post subject: Reply with quote
fermy wrote:
RichA wrote:

It wasn't a price thing. They couldn't make fluorite crystals in the sizes needed for some of these lenses. Crown glass with thorium was easy. Until Canon and Takahashi (telescope maker) started using fluorite in their products in large sizes. Even so, at $600/lb, making a 10" wide, 15lb fluorite element for a Kodak Aero Ektar aerial surveillance lens would have been pricier than thorium which is cheap. Also, all good lenses need to be recomputed for each glass batch as they vary in characteristic.


Sure, price was not the only consideration. For instance, before the use of computers became practical in the field, calculating an extra corrective element was very difficult, sometimes prohibitively so. However, approximately from the end of 1950s the use of thorium in consumer lenses was primarily to save costs.


Consumer lenses, probably. Kodak Pony instamatic cameras had thorium lenses too.


PostPosted: Sat Jun 03, 2017 8:02 am    Post subject: Reply with quote
Ah'd argue that the use of Thorium (and Lanthanum) was tae improve the lens quality and that lower cost was a serendipitous, secondary reason. Lenses like early Summicrons (f2),Canons, SMC Tak, Super Tak, Super multi coated Tak and Yashinon DS were hardly cheap consumer lens. Initially, it was about improving lens quality not a drive tae reduce cost/price...IMO... Like 1 small

Last edited by TAo2 on Sat Jun 03, 2017 4:51 pm; edited 1 time in total


PostPosted: Sat Jun 03, 2017 12:43 pm    Post subject: Reply with quote
RichA wrote:

That came from a manufacturer of high-end telescopes.


Takahashi?


PostPosted: Sat Jun 03, 2017 2:10 pm    Post subject: Reply with quote
Whoa! I just wanted to create new topic, but then I saw this one right in time.
I have small question about lenses with radioactive elements: does they ring on airport scanner ?
I mean had anyone such experience?
I `ve recently bought SMC Takumar 50 1.4 and wanted to take it to vacation by plane. Is there chance that it will trigger scanner during airport security check ?
Thank you!


PostPosted: Sat Jun 03, 2017 3:54 pm    Post subject: Reply with quote
TAo2.......Indupitably Wink


PostPosted: Sun Jun 04, 2017 11:19 am    Post subject: Reply with quote
gud wrote:
Whoa! I just wanted to create new topic, but then I saw this one right in time.
I have small question about lenses with radioactive elements: does they ring on airport scanner ?
I mean had anyone such experience?
I `ve recently bought SMC Takumar 50 1.4 and wanted to take it to vacation by plane. Is there chance that it will trigger scanner during airport security check ?
Thank you!


That depends. I've flown with radioactive Nikkor-N 35mm f1.4 without triggering airport alarm. Here are accounts of other people who had a similar experience. http://www.rangefinderforum.com/forums/archive/index.php/t-150550.html At the same time, I know several cases of people with Takumar's being stopped at Russian airports and one case of someone with radioactive CZJ lens being stopped at Ukrainian airport.

I guess as long as you travel in Europe/US, you are probably safe, however there could be surprises in more exotic countries.


PostPosted: Sun Jun 04, 2017 1:03 pm    Post subject: Reply with quote
fermy wrote:


That depends. I've flown with radioactive Nikkor-N 35mm f1.4 without triggering airport alarm. Here are accounts of other people who had a similar experience. http://www.rangefinderforum.com/forums/archive/index.php/t-150550.html At the same time, I know several cases of people with Takumar's being stopped at Russian airports and one case of someone with radioactive CZJ lens being stopped at Ukrainian airport.

I guess as long as you travel in Europe/US, you are probably safe, however there could be surprises in more exotic countries.


Thank you for the link! Yes, I already studied couple videos from RU\UKR net about this case. In UKR, there is a law that forbids to store and transport Thorium-consisting consumer goods, so security uses this law to press one`s they were able to caught. From other perspective, there are some thorium Taks on UKR market from time to time, this means that someone smuggling them into country anyway.


PostPosted: Mon Jun 05, 2017 1:01 am    Post subject: Reply with quote
gud wrote:
Whoa! I just wanted to create new topic, but then I saw this one right in time.
I have small question about lenses with radioactive elements: does they ring on airport scanner ?
I mean had anyone such experience?
I `ve recently bought SMC Takumar 50 1.4 and wanted to take it to vacation by plane. Is there chance that it will trigger scanner during airport security check ?
Thank you!


I shipped a very hot (large) Kodak Aero Ektar to Hong Kong and there were no problems. Owing slightly radioactive lenses is completely legal an no threat to anyone. In fact, you can own legally (in U.S.) up to 10 POUNDS of uranium oxide or thorium oxide, but you'd have a tough time finding it.


PostPosted: Mon Jun 05, 2017 4:08 pm    Post subject: Reply with quote
Well, in Ukraine/Russia they still have some leftover laws from Soviet times, when sneezing was not completely legal and idiotic/corrupt customs officers that sometimes decide to apply them (most likely hoping for bribe). Of course, people are bringing Takumars in. In fact, I flew with my Nikkor to Ukraine with no issues, did not imagine at the time that it could be a problem, but apparently it can.


PostPosted: Sun Jun 11, 2017 2:33 pm    Post subject: Reply with quote
Optical glasses with radioactive thorium oxide have been researched since the 1930s. The objective of these researches was to achieve a high index of refraction, above 1.7, not very low dispersion, which is only possible for optical glasses with a refractive index below 1.55. High refractive index are used to make lenses with moderate curvatures, which reduces spherical, astigmatism and coma aberrations. Glasses with high refractive index are therefore important in the design of high-speed normal and wide-angle lenses.

The figure below, taken from a Kodak patent of 1939, shows some thorium glasses. The table shows that several other rare-earth compounds were used in the composition of such glasses.





The dispersion index (Abbe number) of Kodak glasses are around 45~50, which qualifies them as medium dispersion glasses. The greater the Abbe number, the smaller the dispersion. The highly dispersive flint glasses can have Abbe number as low as 21. On the other hand, optical glasses of really low dispersion can have Abbe numbers greater than 80.

The figure below shows the optical glasses produced by Schott. Note the extremely low-dispersion FK glasses, which are used in fast super-telephoto lenses. The Abbe number of the 51A is about 85, but the refractive index is only 1.49.



PostPosted: Mon Jun 12, 2017 1:32 am    Post subject: Reply with quote
Himself wrote:
RichA wrote:

That came from a manufacturer of high-end telescopes.


Takahashi?


Astro-Physics uses six-sigma fluoro-crown glass, FPL-53 by Schott. Takahashi used pure fluorite back when. Jury is still out IMO, as to what they actually use today.


PostPosted: Mon Jun 12, 2017 1:35 am    Post subject: Reply with quote
Gerald wrote:
Optical glasses with radioactive thorium oxide have been researched since the 1930s. The objective of these researches was to achieve a high index of refraction, above 1.7, not very low dispersion, which is only possible for optical glasses with a refractive index below 1.55. High refractive index are used to make lenses with moderate curvatures, which reduces spherical, astigmatism and coma aberrations. Glasses with high refractive index are therefore important in the design of high-speed normal and wide-angle lenses.

The figure below, taken from a Kodak patent of 1939, shows some thorium glasses. The table shows that several other rare-earth compounds were used in the composition of such glasses.





The dispersion index (Abbe number) of Kodak glasses are around 45~50, which qualifies them as medium dispersion glasses. The greater the Abbe number, the smaller the dispersion. The highly dispersive flint glasses can have Abbe number as low as 21. On the other hand, optical glasses of really low dispersion can have Abbe numbers greater than 80.

The figure below shows the optical glasses produced by Schott. Note the extremely low-dispersion FK glasses, which are used in fast super-telephoto lenses. The Abbe number of the 51A is about 85, but the refractive index is only 1.49.



Some glasses despite their advantageous dispersion characteristics can't be used owing to susceptibility to atmospheric attack. Fluoro-crowns are fine and are used in varying grades in many lenses and telescopes. Fluorite, which has been the subject of old wives tales concerning "thermal shock" and weathering is also fine, but ideally, it should be inside the camera lens and not an exposed outer element as it is soft (MOH hardness 4 versus 5 for most glasses) and could suffer if exposed to acidic water. Better safe than sorry.


PostPosted: Mon Jun 12, 2017 3:18 pm    Post subject: Reply with quote
Been flying a few times within Europa with my Porst 1.2/55 mm, which shows ~ 40 µSv/h at the back mount. But not a lot if you move further away (no surprise). From what I could find online, most detectors will go for gamma or neutron. That's the reason for people with 131-iodine or thallium scans triggering the scanners.
So depending on the sensitivity, a lens might trigger a gamma detector. I wonder which device triggered the incident at the Ukraine airport. Anybody has more info?
Anyway, even though I like my radioactive lenses, I am probably not going to travel with them in my backpack. I am already receiving "random" security checks almost all the time when visiting the US. I don't wan't to be questioned by Homeland Sec or have my lenses taken away...
Edit:
Wrapping the radioactive lens in thin sheets of lead might work. Alpha emitters do not produce Bremsstrahlung the Radium emits gamma. However, I would think that this approach might be even more suspicious to security.

Last edited by Miles Teg on Tue Jun 13, 2017 8:27 am; edited 1 time in total
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