An m42 (Praktica) mount Vivitar 28mm – made by Kiron
Users of 1970s era Vivitar lenses are usually aware that Vivitar did not manufacture their own lenses. Camera-wiki.org has provided a list of the actual manufacturers as discerned by the first two digits of the lens serial number. Camera-wiki offers your basic CYA disclaimer so that none dare call the list gospel. Nonetheless, its utility is obvious. I regularly use a Vivitar wide angle (an M42 mount 28mm) that is prefixed with the number 22. The fact that this lens was made by Kino/Kiron explains why the optics are so impressive.
Vivitar Serial Number Prefix Codes