Zeiss's classic fast Sonnar — the post-war Opton 50mm f/1.5 adapted to Leica Thread Mount.
The Opton Sonnar 50mm f/1.5 is a West German post-war Zeiss fast normal, from the era when Oberkochen lenses carried the Opton marking. Examples adapted to Leica Thread Mount let this classic Sonnar formula be used on screw-mount and adapted rangefinder bodies. It descends from the pre-war Zeiss Sonnar design.
It is a manual-focus rangefinder-coupled lens with a 50mm focal length and a maximum aperture of f/1.5, built on the classic Sonnar optical layout. Native Zeiss Sonnars of this type were made in Contax rangefinder mount; the LTM examples here are screw-mount conversions or adaptations of that design.
The Sonnar formula is known for smooth rendering and low flare with strong central sharpness wide open, and a characterful transition to the background. At f/1.5 it suits portraits and low light, with contrast and edge sharpness improving as it is stopped down to middle apertures.
On the used market these are vintage optics, so inspect carefully for haze, cleaning marks, coating wear and separation between cemented elements, and check the focus feel and aperture for oil. Adaptation quality varies on converted lenses, so verify rangefinder coupling and infinity focus. It adapts to Leica M with an LTM-to-M ring and to mirrorless cameras via an adapter.