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Published on Sep 6, 2011
Lens: Ernst Leitz GmbH Wetzlar Summicron f = 5cm Nr 1023xxx (M39/LTM mount -- 1953?)
This video shows the radioactivity from a Leica M39/LTM 50mm f/2 collapsible Summicron camera lens, as measured by a simple geiger counter with a pancake probe.
Apparently some early collapsible Summicron lenses may have used radioactive thorium-containing glass (type SBC?) from Chance Brothers Glass in the UK. In 1954 this glass may have been replaced with non-radioactive (for all practical purposes) Schott LaK9 glass with similar optical properties.
One source says that early Summicrons with thorium are in the following serial number ranges: 920xxx-922xxx, 993xxx-995xxx, 1009xxx, 102xxxx, and 104xxxx.