Vivitar's 50mm f/1.8 — a common, affordable third-party M42 standard prime.
The Vivitar 50mm f/1.8 is a standard prime sold under the Vivitar brand in M42 mount. Vivitar sourced lenses from various Japanese makers, so build and optics can vary by production batch, but this was a common fast normal lens in their screw-mount range.
This is a manual-focus M42 screw-mount lens with a 50mm focal length and a maximum aperture of f/1.8. Focus and aperture are set by hand on the barrel, with an automatic diaphragm. It is a compact all-metal standard prime. As with Vivitar-branded lenses the maker varied, and detailed element figures are not asserted here beyond the verified focal length and aperture.
As a fast standard the 50mm f/1.8 suits portraits, street and general work, with the bright aperture giving low-light capability and shallow depth of field. Vivitar standards of this type render cleanly with pleasant character, making it a common and dependable everyday normal lens for adapted use.
Used copies are cheap and plentiful, with quality varying by maker. Inspect for haze, fungus and cleaning marks, confirm the aperture blades are clean and oil-free, and check the aperture-ring and focus feel. Verify the M42 mount before purchase. An M42 adapter makes it an affordable characterful standard on mirrorless.