This lens was one of the first manual focus lenses I bought and came as part of a job lot. Due to my lack of experience I expected a poor performance from this lens based on the brand because at the time I had no idea that many of the old manual focus brands were just importers and that this lens was likely to have been made by one of the major Japanese manufactures. In time I came to realise that the lens was probably made by Tokina and that there are Vivitar and Mamiya versions out there as well as others.
I have to add that this lens has several patches of fungus around the perimeter of the front element along with what appears to be some residue possibly from internal lubricants leaking. I have yet to buy a decent lens spanner but when I do I will be able to easily clean the lens up and I would expect the image quality at the edge of the frame to improve somewhat.
All of these samples are wide open:
You can click on the following two to see them at 100% size: