The Jupiter series lenses were manufactured in several different places at different times (KMZ, KOMZ, VOMG). The 21M models seems to have been manufactured at the VOMG plant during the 1970's to 1990's. A few useful reviews and descriptions of this lens are here: [url]https://radojuva.com/en/2013/03/obzor-yupiter-21m-4200/[/url] [url]https://liveviewer.ru/en/2016/12/obzor-obektiva-yupiter-21m-200mm-f4-0/[/url] [url]http://www.legacylens.eu/lens-database/soviet-lenses/jupiter/[/url] [url]https://helios-lens.com/tpost/d72mv9b101-legend-of-soviet-lens-building-jupiter-2[/url] [url]https://helios-lens.com/tproduct/1-423241602991-jupiter-21m-4200-m42-vomz-1985[/url]