While you can see from the pics I have posted that the vivitar 35-70mm f2.8-3.5 is a good lens, when I did some test pics of the castle those highlighted some "decentering* " - pics when scrutinised were softer on the right side. Then I spotted one in PKA mount, which I doubted even existed though a reviewer on the review page reported one. So I was prompted to make a move and put in an offer, this manouvre was successful.
Another nice minty one, and I am now keen to see if this one tests better.
*there are a number of different optical causes of this, decentering as strictly defined (optical lens elements that are either moved or tilted from the principal axis of the lens) is just one, but decentering tends to be used as a generic desciption of a lens showing softer on one side.