The Mamiya / Sekor SX 135mm f/2.8 is a telephoto prime lens for 35 mm SLR cameras with the M42 screw mount.
This is rather a big and sharp lens. It is equipped with a retractable hood. This SX series lens was manufactured by Mamiya for Mamiya "SX" cameras, alongside with lenses for Voigtlander QBM cameras. The optical scheme includes four elements in four groups.