The lens does look a little weak on the right side. The brick wall test is the only one you can draw any conclusions from because it is very important that the test be conducted with the focal plane of the lens exactly parallel to the test target.
You can exchange the lens, but there is a good chance that you will not get one any better than the one you have. I got three 16-50s, the first one was badly decentered, the second one was mildly decentered, and the third one was badly decentered. I may have kept the second one if I had known the third one would be worse.
If you sent it to Pentax, you probably have a better chance of getting a good one back. I thought about doing this, but I had a hard time convincing myself to send a brand new lens in for repair.
Originally posted by Burgerbrater Hi Ash,
I have tested the lens. I am dissapointed. It seems to me that not matter what f stop the right side is now decentered.
I put examples in a picasa album. Would kindly take a look and see what you think.
thanks,
Alex
Picasa Web Albums - alexconrady - Pentax 16-50m...