Mitakon's 135mm f/2.8 was a compact manual-focus telephoto sold through 1970s-80s importers, part of a wave of Japanese-made third-party primes competing on price against 135mm lenses from Canon, Nikon, Pentax and Minolta, aimed at portrait and general telephoto use.
A manual-focus, auto-diaphragm design with multi-coated (MC) optics and a maximum aperture of f/2.8 at 135mm. Surviving examples confirm production in Canon FD mount; broader mount coverage for this specific model is not well documented in period catalogues.
Wide open it renders with soft contrast and a gentle glow typical of 1970s tele designs, sharpening by f/5.6-8. Background blur at f/2.8 is smooth for a lens of its class, making it usable for simple portrait work despite middling edge sharpness.
Supply on the UK used market is thin next to better-known 135mm f/2.8 primes of the period. Inspect the aperture blades for oil contamination, confirm the FD mount tabs and coupling pin move freely, and check the rear element for haze common in vintage barrels.