The whole time I was doing these tests the Tamron was sitting on a few forum sites seeking a buyer. If it did not sell I would finish all sorts of additional tests, and if it did my budget would be in much better shape. It sold today, so the testing has reached an unimpressive conclusion.
This is quite unfair to both lenses, but perhaps mostly to the SP 90mm. Now that I have pinpointed the true center-AF point on my K-5 I should check if that was the reason for the more frequent focus hunting that I experienced with that lens. That was really the closest thing to a complaint that I had, and it probably accounts for many of the Sigma's missed-focus events as well.
So it's really not possible to say either lens is a winner here - I am the overall winner, for several reasons:
- I had two nice lenses to choose from, so no losing for that
- I now have a 50mm lens that I find satisfactory
- I improved the bank balance going from the 90mm to the 50mm
- I have more space in my bag with the smaller, lighter Sigma - and
- I still have a 1:1 macro lens that gives me excellent results!
So farewell to an excellent lens, and greetings to another!