Haven't tried it, Shaun, but here's what was reported a while back:
Pentax lost money on both the FA 50 f2.8 and FA 100 f2.8 macros. So they were redesigned to be less expensive to build. The D FA is reported to keep the same optical design as the F/FA 50 -- and that formula is near legendary. The D FA 100 is a new formula.
I don't recall seeing any reports of any 100 mm. macro that wasn't sharp. Has anyone else? It seems to be a simple thing to design. So the D FA 100 is probably a great lens.
For now I'm keeping my FA 100 f2.8. It gives wonderful results on my D, even at f22. But it is certainly heavy and bulky compared to the new D FA.
Joe
