Radioactive Leica 50mm f2 Collapsible Summicron (M39) good idea as only Lens?

[Anbaric]

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1 hour ago, M9reno said:

However..... collapsible *M-mount** Summicron s.n. 1.115.862 was also thorium-contaminated, even if 4/5 less than its 1951 sibling:  58 counts per 180 seconds (margin of error of 10 counts).  

I don't think I've ever read 1954 M-mount Summicrons were thorium-contaminated. But mine is.

With lenses like the earlier collapsibles, addition of thorium oxide to the glass was deliberate, but when they later switched to lanthanum oxide it has been suggested that contamination with thorium was an issue, especially in some batches of glass. Both oxides were refined from the same ore, monazite, and the process for purifying the lanthanum wasn't perfect. See for example this page on Marco Cavina's old site (in Italian).

Edited May 22, 2024 by Anbaric

[S. H.]

Are the radioactive summicron constructed slightly differently? I came across a japanese page that showed some mechanical differences in construction between lenses:

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Are those external differences really correlated to the radioactivity of the glass? I'm interested, because I just bought a summicron in the #1103xxx range that looks like the radioactive variant, and I don't have any geiger counter. I only do BW film so the yellow cast would be lost on me, but the built in contrast would be appeciated.

 

[satijntje]

My collapsible 50mm Summicron from 1957 (serial 1480XXX) has a dot and not a comma at the 2.8.
I do not consider my lens to be radioactive as I do not see any signs of this.

It is indeed a very nice lens, very small to transport it and it has a lovely rendering.
I need to practice with this lens as I received it only yesterday 🙂

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[PG Black nickel]

Unfortunately for us ... with Leica nothing is ever certain!
For example on the summicron SOOIC M with a very old number (9204xx-9205xx) with thorium it is 2.8 and not 2,8
But that's probably because it's the M series.

the image is that of the 9204xx

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[Anbaric]

2 hours ago, PG Black nickel said:

Unfortunately for us ... with Leica nothing is ever certain!
For example on the summicron SOOIC M with a very old number (9204xx-9205xx) with thorium it is 2.8 and not 2,8
But that's probably because it's the M series.

the image is that of the 9204xx

Is this one a confirmed (significantly radioactive or yellowed) thorium lens? I see it doesn't have the 'step' between the aperture numbers and their index markers that is usually associated with the thorium lenses (as on the Japanese site quoted above).

Edited May 26, 2024 by Anbaric

[Anbaric]

3 hours ago, S. H. said:

Are those external differences really correlated to the radioactivity of the glass? I'm interested, because I just bought a summicron in the #1103xxx range that looks like the radioactive variant, and I don't have any geiger counter. I only do BW film so the yellow cast would be lost on me, but the built in contrast would be appeciated.

Is yellowing visible in this lens? If so, I imagine that on its own is a pretty good indication of thorium (though its absence wouldn't necessarily mean it is not radioactive, as the yellowing could have been bleached with UV).

[S. H.]

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9 hours ago, Anbaric said:

Is yellowing visible in this lens? If so, I imagine that on its own is a pretty good indication of thorium (though its absence wouldn't necessarily mean it is not radioactive, as the yellowing could have been bleached with UV).

I think there is a slight yellow or brown cast, but I'm not sure. Being a later example it has a purple antireflective coating, so hard to tell... The glass is not plain yellow like some other radioactive  summicrons.

According to the seller it sat for a long time in a glass case. He said nothing about radiation.

[PG Black nickel]

I don't have a meter to measure the level of radioactivity, but it seems to me to have a characteristic yellow colour, although I have the impression that this colour is fading because the camera and its lens have been in a display case for a few years without a cap on the lens.

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