Chinon — 28mm f/2.8 wide-angle prime for M42, later offered in Pentax K, Minolta MD and Olympus OM
Chinon Industries was a Japanese SLR and lens maker based in Suwa, Nagano, active from the early 1970s into the 1980s alongside bodies like the CE Memotron and CE-4. The 28mm f/2.8 was a standard wide-angle prime in its range, also sold under the Chinar house brand for other retailers.
It was sold mainly in M42 screw mount alongside Pentax K, Minolta MD, Konica AR and Olympus OM versions, used a 6-blade auto diaphragm from f/2.8 to f/22, focused to about 0.4m, and carried a 52mm to 55mm filter thread (some examples measure 62mm). Weight is reported at roughly 250g to 290g.
Wide open it showed gentler contrast and soft corners typical of 1970s independent wide-angles, sharpening by f/5.6-f/8, with some veiling flare into bright light from its period coatings. One period review rated it capable but short of the contemporary Pentax Takumar 28mm f/3.5.
As a common OEM-era lens rather than a collectible, it sells cheaply on the UK used market. Check the aperture blades for oil, confirm the auto/manual switch and click stops work cleanly, inspect for rear-element haze, and verify the mount, since the same design carries several badges.