Collapsible Summicron 50mm f2. The Leitz product code is SOOIC.
This example is the so-called radioactive Summicron that uses thorium glass. A Geiger counter test confirms that it shows a noticeably strong reading. Serial number is in the 1.04 million range, made in 1952, with meter scale.
It appears that two elements in this lens are made of thorium glass. As is typical, the glass has yellowed, which can give slightly stronger contrast when shooting in monochrome. Comparing it with a later non-thorium Summicron would certainly stimulate one’s curiosity.

Minor scuff marks are visible on the front edge of the barrel and around the base, but there are no noticeable scratches or dings. The lens received a full overhaul including focus calibration in November 2025, and thanks to careful servicing, all controls now operate smoothly. The collapse mechanism locks with a pleasant, appropriate torque, making operation stress free. Rangefinder coupling is perfectly aligned.
The glass shows very faint cleaning marks on both the front and rear elements, and slight edge-localized coating wear on the inner element, but none of these affect real-world photography. For a thorium Summicron, which often suffers from rough or heavily aged glass, this is a remarkably clean example. You can enjoy the characteristically crisp rendering and razor-sharp focus that this radioactive Summicron is known for.
Comes with a Leica front cap and a third-party rear cap.