Vivitar is (was) an interesting company. Now adays, it's known for cheap and crappy lenses and accessories. But, in its hay days of the 70s, they designed some of the best lenses of its time, and eventually become cult classics. They were never a manufacturing company, but they hired some very bright optical designers to create interesting lenses. These lenses were manufactured by many different companies, including Tokina, Schneider of Germany, Perkin Elmer of US, and Kino, Olympus, among others. Their most famous line was the Series 1. Lenses bearing this mark usually have excellent optical quality, like the Canon's L lenses.
Vivitar made Many versions of the 28mm focal length. I have owned the 28mm f2.8, 28mm f2.5, 28mm f1.9 (Series 1), 28mm f2.0. By the the best known of the 28mm is the Series 1 28mm f1.9, which I have in a Minolta MD mount.
Yesterday I acquired the 28mm f2 in Nikon Ai-S mount. Lens was made by Komine, as the serial # suggests (28xxxxx). This very compact lens has a 49mm filter thread, small for a lens this fast. A unique feature is the close focusing capabilities, which makes for some interesting effects. For one thing, you can actually get very defocused background if you shoot at minimum focus distance. In fact, the bokeh is not bad at all. At slightly longer distance, you can get a lot of background but still have a subject fill most of the frame.
For the couple dozen of shots I did last night, I am amazed at how sharp this lens is wide open! Definitely better than most 28mm lenses from its time. Will shoot some more to assess the image quality later on.
Untitled -- 5D & Vivitar 28mm f2 @ f2. Larger Picture.
Canadian Opera Company -- 5D & Vivitar 28mm f2 @ f2.5. Larger Picture.