Mamiya's Sekor 50mm f/2 SX — a compact Japanese M42 standard prime from the SX system.
The Mamiya-Sekor 50mm f/2 SX is a Japanese standard prime made in M42 mount by Mamiya. The SX designation marks the later Mamiya screw-mount system with its open-aperture metering coupling, and this was a standard normal lens within that range.
This is a manual-focus M42 screw-mount lens with a 50mm focal length and a maximum aperture of f/2. Focus and aperture are set by hand on the barrel, with an automatic diaphragm and the SX metering coupling. It is a compact all-metal standard prime. Detailed element figures are not asserted here beyond the verified focal length and aperture.
The 50mm standard view suits portraits, street and general photography, with f/2 giving useful low-light performance and moderate subject separation. Mamiya standards of this era render cleanly with pleasant character, and the compact SX design makes it a tidy everyday normal lens for adapted use.
Used copies are affordable and less common than the mainstream standards. Inspect for haze, fungus and cleaning marks, confirm the aperture blades are clean and oil-free, and check the aperture-ring and focus feel. Note the SX coupling pin when adapting, as it may need clearance. Verify the M42 mount. An M42 adapter allows use on mirrorless cameras.