Archived posting to the Leica Users Group, 1999/08/24

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Subject: [Leica] Yellowing glass in retractable Summicron
From: "Doug Richardson" <doug@meditor.demon.co.uk>
Date: Tue, 24 Aug 1999 10:31:53 -0000
 
We've had a lot of discussion on the subject of the possible use of
radioactive thorium-based glass in some Leitz lenses.

Bill Rosauer wrote:

>Hold your LTM Summicron over a white piece of paper and look through
it. If
the lens has a yellowish cast, this is most certainly one of the early
Summicrons in which radioactive thorium was one of the "rare" earth
elements
used in making the glass. Apparently, this warm yellowish cast is part
of
the decaying process of the thorium.

On Sunday I tried this test with my own recently-purchased 5cm
retractable Summicron, and yellow it most certainly is. No point in
trying to shoot Kodachrome with this one!

Does anyone know is this type of glass was used in all 5cm retractable
Summicrons?

Regards,

Doug Richardson