Mir's 20 20mm f/3.5 — a Soviet M42 ultra-wide-angle rectilinear prime.
The Mir-20 20mm f/3.5 is a Soviet ultra-wide-angle prime made in M42 and other mounts. It was the wide-angle Mir option covering a 20mm rectilinear field of view, serving photographers needing broad coverage on Soviet SLR systems.
This is a manual-focus M42 screw-mount lens with a 20mm focal length and a maximum aperture of f/3.5. Focus and aperture are set by hand on the barrel and it is a retrofocus wide-angle of all-metal construction. Exact element counts and filter figures are not asserted here beyond the verified focal length and aperture.
At 20mm it delivers a genuinely wide rectilinear view for landscapes, architecture and interiors, with generous depth of field from the f/3.5 aperture. Soviet ultra-wides of this type render acceptably stopped down and are chosen for the breadth of coverage they give at modest cost compared with Western equivalents.
Used copies are less common than the standard Soviet primes and priced above them. Inspect the front element for scratches, haze and fungus, confirm the aperture blades are clean and the ring works, and check focus. Verify the mount is M42. An M42 adapter allows wide-angle use on mirrorless cameras.