I used to own the Kiron 105/2.8PK; I now own the Tokina AT-X 90/2.5PK. The Kiron didn't deliver sharp results until about f/5.6. That's why I sold it; I use my portrait-length lens for general purpose, including shooting indoor events under available light.
The Tokina is very sharp, even at f/2.5. I get such sharp results at f/2.5, I almost feel as though I'm cheating. Its colors are noticeably snappier and more saturated, too. Note that the Tokina 90/2.5 focuses in the same direction as Pentax; the Vivitar 90/2.5 does not. However, the Vivitar's 1:1 macro adapter has a built-in tripod ring, unlike the other macros discussed in this thread. Of course, you could match the Vivitar's adapter with the Tokina lens. [EMAIL PROTECTED]
