Well, I just received the Tamron 28-75 and did some rough testing at 28mm, 50mm, 70mm at f2.8 f4 and f5.6.
Overall the FA* has much better rendering, sharper and the bokeh is never nervous, The Tamron is very good (even better than the FA* at 70mm at f2.8 wherer the FA* zoom is very very weak), but lags behind the FA* zoom slightly. The Tamron is less sharp, the bokeh at times can be a bit nervous but still very good. Overall pictures do look better with the FA*.
Here are a couple of sample shots at f2.8 and f4 at 50mm.
CLICK ON THE IMAGE FOR FULL RESOLUTION
Tamron 50mm f2.8 (Focus on the puppet's left eye)
Pentax 50mm f2.8
Tamron 50mm f4 (I took a shot of the glass, as fine lenses like the limiteds and the FA* render glass to look like real glass)
Pentax 50mm f4
Last edited by pcarfan; 05-19-2010 at 06:29 PM.