Sigma 24-50mm f/4-5.6 — compact manual-focus wide-to-standard zoom from the early 1980s.
The Sigma 24-50mm f/4-5.6 was a compact manual-focus wide-to-standard zoom from the early-to-mid 1980s, aimed at photographers wanting a wider starting point than the common 28mm kit zooms of the period.
Covering 24-50mm with a one-touch push-pull zoom and manual focus action, it used a variable f/4-5.6 maximum aperture in a relatively small barrel for its range. Sigma made it in a spread of fittings including M42, Pentax K, Canon FD, Nikon F, Minolta MD, Olympus OM, Konica AR and Contax/Yashica mounts.
The wide end suits landscape and interior work, though corner sharpness and contrast drop off toward 24mm and at maximum aperture, tightening up once stopped down to the middle of the aperture range.
Secondhand copies are uncommon compared with more popular Sigma zooms of the era. Check the zoom ring for smooth wide-to-tele travel, verify aperture blades move without oil, and inspect for haze given the lens's age.