Sigma 75-210mm f/3.5-4.5 — early manual-focus telephoto zoom, predecessor to the 70-210mm.
The Sigma 75-210mm f/3.5-4.5 predated the better-known 70-210mm in Sigma's manual-focus telephoto zoom catalogue, sold through the late 1970s and into the early 1980s as an entry-level reach option for SLR owners.
It covers 75-210mm through a push-pull manual zoom and focus action with a modestly variable f/3.5-4.5 maximum aperture, built in an all-metal barrel typical of the era. Sigma made it available in fittings including M42, Pentax K, Canon FD, Nikon F, Minolta MD/SR, Olympus OM, Konica AR and Contax/Yashica mounts.
Rendering is soft wide open and at the long end, improving markedly by f/8, giving results closer to a basic telephoto than a refined optic, though adequate for casual sport, travel or wildlife shots at modest print sizes.
Values are low on the secondhand market. Check the push-pull zoom collar for wear and slop, confirm the aperture ring detents are intact, and examine the rear element for the haze common in older Sigma tele zooms.