Originally posted by thibs
BTW did you test your 50-135 with K10D firmware <1.3 ?
The little time I played with one (not using SDM) I felt it was very quick and quite silent for a non-SDM lens (and I was in a poorly lit shop).
I'm curious.

I have tried it fot two days before upgrading to v1.3, since then, I also tried the lens on my Ds and my Z1P.
I find the AF speed to be about the same with/without SDM so I don't think the relatively unimpressive AF speed is related to SDM.
It's more of a design/gearing issue IMO.
Don't get me wrong though, I am using it extensively now and the lens won't go anywhere as it is really an excellent lens, the AF speed "issue" doesn't really show up until you want to focus quicly from far to near. But if you have to do this, it take about 1s to go from 1m+ to 10m+ which is not very good, even by Pentax standards (which are pretty good IMHO).
My FA 135 take approximately half of that time to go from 0,7m to infinity on the K10 and more generally, all my lenses are faster to travel from their min focusing distance to infinity (DA 12-24, FA 50, DA 50-200, Sigma 170-500 & 17-35) so... it's a little bit unexpected for the new high-end Pentax f2.8 telephoto that is supposed to bring us equivalent technology/performances to 70-200s USM/AF-S offerings from the competition...