The Jupiter-8 (sometimes marked in Cyrillic, ЮПИТЕР-8) is a 50 mm f/2 lens made by KMZ in the years after the Second World War. It is a close copy of the Zeiss Sonnar, with six elements in three groups; the Soviet Union took the design data for several Zeiss products in War reparations (equipment, and even staff, were also taken to the Soviet Union). The Sonnar had been the standard lens for the Contax, and the J-8 became the standard lens for the Kiev, the Soviet copy of it.
KMZ originally made the Jupiter-8 for the Kiev; it was made by the Arsenal factory from about 1956. KMZ also made the J-8 in an M39 screw mount for its Zorki rangefinder camera series: it first appeared on the Zorki 3 in 1953, and later was the standard lens on the Zorki 3S. Both versions of the lens appear in a 1949 lens catalogue.
The J-8 was originally made with a polished aluminium barrel, though some examples exist in stainless steel. From the 1970s, the lens was made in a black finish (the barrel is still aluminium).
Optical formula, from OPAL database