Like much of the gear sold under the names of companies that marketed but did not manufacture goods, Vivitar lenses are a mixed bag (though Vivitar, in this case, is given credit for the designs). Here is a website that lists the companies that did the manufacturing for them during the period from 1970 to 1990. I have found the Kiron lanses to be quite good (serial numbers beginning with 22), but others may have a different experience.