Zeiss's compact Sonnar normal — the 50mm f/2 adapted to Leica Thread Mount.
The Sonnar 50mm f/2 is a classic Zeiss normal built on the Sonnar optical formula, a design famous from the pre-war and post-war Zeiss rangefinder line. Examples in Leica Thread Mount allow this compact fast normal to be used on screw-mount and adapted bodies. Native versions were made in Contax rangefinder mount.
It is a manual-focus rangefinder-coupled lens with a 50mm focal length and a maximum aperture of f/2, using the Sonnar layout that is more compact than a comparable double-Gauss design. The LTM examples here are screw-mount conversions or adaptations of the Zeiss Sonnar.
The f/2 Sonnar is known for smooth tonal rendering, good flare control and pleasing background blur, with strong central sharpness even wide open. As a moderate-speed normal it suits portraits, street and general use, tightening across the frame when stopped down a couple of stops.
These are vintage lenses, so check thoroughly for haze, internal cleaning marks, coating scratches and any element separation, and test the focus feel and aperture for oil. On converted examples confirm rangefinder coupling and correct infinity focus before buying. It adapts to Leica M with an LTM-to-M ring and to mirrorless bodies via an adapter.