OK, I know this is totally apples-&-oranges here, but I have the Tokina 12-24 f4 on a Nikon DSLR mount and have been very happy. The build quality is exceptional, it performs great optically, and while I know this doesn't apply to the 28 you're looking at, the autofocus is fast and accurate. I wouldn't hesitate to buy another Tokina lens.