Originally posted by tbirdas I really wonder whether the lenses make all the difference in AF. All my Pentax lenses are screw-driven while only a couple of Nikon are. I have an order for the 18-135 and I am curious to see
They really do.
I had an 18-135 for a while, and with its DC motor it's the quickest and quietest focusing Pentax lens I've ever used.
Having moved to the K-5 from the K10D, I'd say the AF is significantly if not enormously quicker with my screw-drive lenses. But the 18-135 is quicker than any of them. The quietness contributes to the subjective impression of speed too.
That said, I tried a 60-250 a few days ago, and its focusing (even though SDM) was slower than my screw-drives (FA50 1.4, DA55-300, DA 18-55 Mk1).
So the lens definitely makes a big difference.
I have no comparative brand experience, so that's as far as my ability to comment goes.