MTO's 500 500mm f/8 — a classic compact Soviet M42 catadioptric mirror telephoto.
The MTO-500 500mm f/8 is a Soviet catadioptric mirror telephoto lens made in M42 and other mounts. One of the classic Soviet mirror lenses, it used a Maksutov-type design to fit a 500mm focal length into a short, portable barrel, giving long reach at low cost and weight.
This is a manual-focus M42 screw-mount catadioptric lens with a 500mm focal length and a fixed effective aperture of f/8. As a mirror lens it has no adjustable diaphragm, so exposure is controlled by shutter, ISO or filters, and focus is by hand. It is a compact, stout lens for its reach. Exact weight and element figures are not asserted here beyond the verified focal length and aperture.
At 500mm f/8 the lens reaches distant wildlife, sport and landscape detail in a very compact package. Mirror lenses render out-of-focus highlights as distinctive rings owing to the central obstruction, and the fixed aperture and manual focus suit deliberate shooting, ideally from a tripod for sharp results at this focal length.
Used copies are affordable and among the more common Soviet mirror lenses. Inspect the mirror optics and front glass for haze, fungus and coating problems, confirm smooth focus, and check the mount and any tripod fitting. There is no aperture to test. An M42 adapter allows compact long-lens use on mirrorless with a support.