Originally Posted by mtngal
The fact that you can't MANUALLY focus it and get something sharp makes me question whether the problem is the SDM/AF mechanism at all - it may be, but then it may not be. My first copy of the DA 55-300, a non-SDM lens, was a piece of junk, too. It wasn't sharp at all until about f16 or so. It focused all right, but the lens had bad optics.
On the other hand, I now have 3 outstanding lenses that are SDM. We'll see today if the replacement DA*16-50 is any better than the first one I returned.
Hope it works out well for you!