[dgaies]

The K20d, K200d, K-m, K-7 can't. Don't know about the K-5 and K-x. The first version firmware of the K10d can. Pentax would need to do a firmware patch to allow screwdrive. I was concerned enough about SDM that when I got a DA* 300mm at the beginning of the year, I paid $60 for a 3 year warranty.

Neither the K-5 nor the K-x (nor K-r for that matter) can use choose to use the screwdrive of a dual-drive SDM lens (basially any SDM lenses except the 17-70 and 55 IIRC).

Too bad, as it would be nice to have that option, both as a backup if the SDM fails and as a potential user option if the screw drive turned out to be faster than SDM for a given lens.

[SylBer]

I know a lot of people experienced SDM failure (by the way, anyone know what is aproximatly the percentage of failure?), but there are people, like myself, who never encountered any problem. I own a DA* 50-135, a DA* 200 and a DA* 300 and their performance is really good. Yes, the DA* 50-135 is a little slow, but the other two are very fast and accurate. And the 50-135 is also very acurate. Finally,if you have a K10D like I do, you can always downgrade the firmware to the version 1.1 and get it to use the screw instead of SDM

[tarsus]

Thanks for this thread. I was set to get the 18-135 until I found out it is SDM or a the least another version of SDM. There is no question that SDM by Pentax is a flawed design. Where the failure is, is their absolute silence on the issue (if I'm wrong here please correct me). I got the Sigma 18-125. Pentax makes the best bang for the buck cameras on the planet, but SDM and their ignoring the problem does not speak well.

[SteveM]

We don't hear many complaints from newer SDM lenses, so it would appear that Pentax has quietly corrected the issue. The new 645d lenses use SDM, so it is safe to presume that SDM is here to stay.

DC is used in a non-sealed (less weather resistant) lens. Presumably it is a weaker / cheaper motor that deals with fewer lens seals.

I do agree however that a newer generation of SDM is needed for performance reasons.

[Pentaxor]

I believe I would prefer the DC. although still untested for durability, it is almost as quiet, if not better and yet much faster than the SDM. I would agree that the successor to the SDM should be faster and durable. otherwise it would be pointless to have an AF lens if you are going to shoot manual doing action/candid photography.