Group,
I found a lens (actually several of them with slightly different focal length) which is marked "Steinheil München f=725mm Quarz" and it indeed seems to to made of Quartz (Quarz is same in German).
It looks quite similar to this one I found years ago:
Any idea what this could have been used for? I read in a book about Steinheil that they made Quartz lenses from natural Quartz found in the Alpes and later Brazil.
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