Quote: Jasvox: Not only sharper and faster, but more contrast and better colors too, in my opinion. I love this lens....even thought about upgrading further (16-50*), but haven't found a good enough reason yet to consider that lens over the 17-50.
The 17-50mm is a remarkable lens--prime-like sharpness, to the edges. I spent a couple of months researching my walk-around lens back when I bought the K20d. I wanted the da 16-50mm, mainly because of the weather sealing, but after doing my homework, I learned the Tamron beat the Da in most categories--I'm talking scientific testing like distortions, sharpness, wide open utility, CA control.
But the Da obviously has the WR edge. However, the Tamron, in all 4 seasons, has been up and down many, many MTS on the East coast with me and has not failed me--yet anyway.
I think a little common sense is the best Weather Resistance!