Mir's 47 20mm f/2.5 — a fast Soviet M42 ultra-wide rectilinear prime.
The Mir-47 20mm f/2.5 is a Soviet fast wide-angle prime made in M42 and other mounts. It offered a bright f/2.5 aperture at a 20mm rectilinear focal length, making it one of the faster wide-angles of the Soviet lens range for photographers needing broad coverage.
This is a manual-focus M42 screw-mount lens with a 20mm focal length and a maximum aperture of f/2.5. Focus and aperture are set by hand on the barrel and it is an all-metal retrofocus wide-angle. Exact element and filter figures are not asserted here beyond the verified focal length and aperture, following the accuracy standard.
At 20mm with a relatively fast f/2.5 aperture the lens gives a wide rectilinear view usable in lower light, suited to landscapes, architecture, interiors and street work. Soviet fast wides of this type render acceptably stopped down and are valued for the combination of wide coverage and a brighter maximum aperture than most.
Used copies are less common than the standard primes and priced above them. Inspect the front element for scratches, haze and fungus, confirm the aperture is clean and the ring works, and check focus. Verify the M42 mount before buying. An M42 adapter allows wide-angle use on mirrorless cameras.