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Radioactivity of certain lenses

Lens
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#1 Ural

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Posted 02 April 2021 - 19:24

Enna München 28mm f/3.5 Lithagon discussion inspired me to test my lenses for radioactivity. Below are readings of GMC-300E detector, readings correspond to the normal background. Although Meyer-Optik and Optomax turned out to be slightly more “radioactive” than other ones.
Cassar-S 50mm f2.8, 0.16 microsievert/h
El-Nikkor 80mm f5.6, 0.12 microsievert/h
El-Nikkor 105mm f5.6, 0.12 microsievert/h
Meyer-Optik Telemegor 180mm f5.5, 0.20 microsievert/h
Optomax 35mm f3.5, 0.19 microsievert/h
Petri 35mm f3.5, 0.18 microsievert/h
PORST Super Weitwinkel 28mm f3.5, 0.17 microsievert/h

Edited by Ural, 05 April 2021 - 00:56.


#2 OlDoinyo

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Posted 03 April 2021 - 02:39

So you say that these are all just background readings? Have you tested anything known to have thoriated glass?

#3 Cadmium

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Posted 03 April 2021 - 04:37

Seems like the big problem would be if the lens glass fluoresces. No?
Such as these uranium marbles.
Attached Image: geiger_marb_UV.jpg

Inside.
Attached Image: geiger_inside_1.jpg

Edited by Cadmium, 03 April 2021 - 04:45.


#4 Ural

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Posted 03 April 2021 - 19:22

View PostOlDoinyo, on 03 April 2021 - 02:39, said:

So you say that these are all just background readings? Have you tested anything known to have thoriated glass?
I have not yet seen UV capable lenses made of thorium, although I am sure there should be such lenses. Most radioactive lenses were made from 1940 to 1970 just like UV lenses.

View PostCadmium, on 03 April 2021 - 04:37, said:

Seems like the big problem would be if the lens glass fluoresces. No?
Such as these uranium marbles.
Haha yes uranium glass lens should give a very strong colour casts.

View PostCadmium, on 03 April 2021 - 04:37, said:

Inside
Now I know what a Geiger tube looks like. Thanks Steve.

Edited by Ural, 03 April 2021 - 21:09.


#5 Andy Perrin

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Posted 04 April 2021 - 00:58

View PostUral, on 03 April 2021 - 19:22, said:

I have not yet seen UV capable lenses made of thorium, although I am sure there should be such lenses. Most radioactive lenses were made from 1940 to 1970 just like UV lenses.
Nah, the problem is exactly the radioactivity. It causes color centers in the glass, making it absorb very well in UV, which is the opposite of what we want in a UV lens. Just because those lenses were made in the same time period does not imply suitability for UV.

#6 UlfW

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Posted 04 April 2021 - 07:24

View PostOlDoinyo, on 03 April 2021 - 02:39, said:

So you say that these are all just background readings? Have you tested anything known to have thoriated glass?
I have one lens with thoriated glass, a Canon FD 35/2.0 SSD with concave front element.

I get different readings from front and back:
Front: 1.0 microsievert/h
Back: 1.9 microsievert/h

I also tested my uranium glass objects and the most active was a greenish glass bowl that showed 0.8 microsievert/h
Ulf Wilhelmson
Curious and trying to see the invisible.

#7 Ural

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Posted 04 April 2021 - 11:13

View PostAndy Perrin, on 04 April 2021 - 00:58, said:

Nah, the problem is exactly the radioactivity. It causes color centers in the glass, making it absorb very well in UV, which is the opposite of what we want in a UV lens. Just because those lenses were made in the same time period does not imply suitability for UV.
Thanks Andy, maybe there are still some radioactive lenses that work well in upper UV-A. If there are none, then when searching for UV lenses, we can exclude all radioactive lenses from our list.

View PostUlfW, on 04 April 2021 - 07:24, said:

I have one lens with thoriated glass, a Canon FD 35/2.0 SSD with concave front element.

I get different readings from front and back:
Front: 1.0 microsievert/h
Back: 1.9 microsievert/h


Wow, that's a lot according to the GMC-300E instruction. How good is this lens in UV photography? If it is ok, then we have at least one UV capable lens with thoriated glass.

Edited by Ural, 04 April 2021 - 11:37.


#8 UlfW

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Posted 04 April 2021 - 11:46

View PostUral, on 04 April 2021 - 11:13, said:

Wow, that's a lot according to the GMC-300E instruction. How good is this lens in UV photography? If it is ok, then we have at least one UV capable lens with thoriated glass.
I would not like to be close to it for extended periods of time, but it normally lives in a drawer away from where I normally stay.
For occasional photography the accumulated dose will not be that bad.
Much of the radiation will also be stopped by the camera body anyhow.

If this was a viewfinder optic it would be very different!

It is highly unlikely that this lens would be at all usable for UV.
There are two main things that limit UV-transmission.
  • Advanced AR-coatings, if not designed for UV. Each lens surface count.
  • Many types of optical glass with bad UV-transmission. The transmission attenuates more if the glass passed is thick.
The 35/2.0 SSC is an advanced lens with many lens surfaces and much glass to pass:
http://www.mir.com.m...nses/35mmfd.htm
The optical design is difficult to see on that page, but compare the modern designs instead between 35/2.0 and 35/2.8:
Attached Image: Screenshot 2021-04-04 at 13.49.20.png
Attached Image: Screenshot 2021-04-04 at 13.49.34.png

Edited by UlfW, 04 April 2021 - 11:50.

Ulf Wilhelmson
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#9 Ural

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Posted 04 April 2021 - 14:49

View PostUlfW, on 04 April 2021 - 11:46, said:

It is highly unlikely that this lens would be at all usable for UV.
There are two main things that limit UV-transmission.
  • Advanced AR-coatings, if not designed for UV. Each lens surface count.

  • Many types of optical glass with bad UV-transmission. The transmission attenuates more if the glass passed is thick.
Thanks UlfW for the detailed answer. To summarise the discussion, UV lenses should have a simple optical design, glasses should not be thick, should not have advanced AR coating and should not be made of thorium or uranium :-)