Zeiss Sonnar is an optical design that spawned a family of compact wide-aperture lenses. The original Sonnars were made from 1932 to the late 1950s, mostly for Contax Rangefinder but also in other mounts.
Cleaning & lubricating a Carl Zeiss Jena Sonnar 1:2 f=5cm T (Contax mount, aluminum)
Wikipedia page on Zeiss Sonnar
Overview of Zeiss Sonnar 50mm f/1.5
Overview of Zeiss Sonnar 50mm f/2
