Originally posted by aslyfox if I am not mistaken, Vivitar was a name and their lenses were built by others
That is basically correct. The original Vivitar was a brand name for a line of photography products produced for and sold by Ponder and Best, a U.S. company. The lenses were made to specification by various manufacturers (Japanese and otherwise) based on designs commissioned by Ponder and Best with intent of matching the performance and build of camera manufacturer's product. For a significant number of years, lens serial numbers encoded both maker and year/week of manufacture with the result that some maker's lenses have developed a better reputation within the brand. Lists matching serial numbers with makers exist at several locations on the Web. I like the article on the Camera Wiki site best:
Vivitar serial numbers - Camera-wiki.org - The free camera encyclopedia
Those made by Schneider, Komine, Kino/Kiron, Tokina, and Perkin Elmer are held in higher esteem. I own a handful* of Vivitar lenses, all of which have excellent build with performance equivalent to the norm at the time for 1st-party offerings from the major manufacturers.
Addendum: It should be noted that some Vivitar models correspond to lenses marketed under the maker's brand as well as the Vivitar name. Conventional wisdom is that the situation was similar to that of the current Pentax D FA 50/1.4 and Tokina Opera 50/1.4 where design and development was done in collaboration with both entities permitted to sell under their own brand.
Steve
* 28/2.5 M42 (Kiron), 28/2.5 Pentax-K (Komine), 135/2.8 M42 (Komine), and 28/2.8 Exakta (unknown)