The early Vivitar lenses were all superb and designed by Vivitar themselselsves although manufacture was sub-contracted. But the brand name changed ownership and some cheaper Vivitar lenses were just rebranded lenses from lesser known manufacturers.

In the 70's to the 90's there were some poor quality lenses from companies like Sigma and Hoya, which you'd have expected to be good. In Hoya's case they had to scrap their entire range and they've not sold lenses under the Hoya name since - instead they used their Tokina brand name and the result was the ATX series.

There were a miriad of odd brand names as well, some just available in one country, so the same lens would appear with a whole host of different nams on it, the 19mm f3.8 vivitar was one of these.

Ian