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.
Rare Leica 50mm Summicron-M f/2.0 lenses: The 'prototype' version in black. Here is a Leica Summicron M 50mm f/2 Rigid Black Chrome made for Leica M4 black. It's not a black paint model but a kind of prototype made for the last version of Leica M4 Black paint, and Leica M4 black chrome. I decided that as far as my next purchase for lenses I wanted to pickup a small set of Leica-R's (likely after I save up for an Epic) I was thinking of only the Summicron 35, 50, 90 for now.