Vivitar 50mm f1.9 Auto
This lens' serial # starts with a 97. After some research I am sure it is a Cosinon.
It is well built lens, mostly metal with a rubberized grip.
The light was dismal for these shots. The lens did well.
My copy has cleaning marks and a scratch on the rear element. From what I've seen so far, that damage doesn't matter. The lens is sharp, very sharp in the center. Edges are soft at wide apertures, but it works for this lens.
At f1.9 it is soft. At f2 it is sharp and contrasty. It's as if they buit this lens from overstock parts. If they limited the aperture to f2 it would be a cult classic. Corners tend to be soft.
Bokeh is soft then swirly, much like a Russian lens. The combination of bokeh and mixed sharpness creates images with character. Like I said, cult classic.
Shadow detail is good. Colors are a tad muted but easily corrected in processing. Overall contrast is excellent. I did not have an opprtunity to test flare. I did not notice any fringing whatsoever on any of my test pics.