Peter,
I'm very sorry to see you this frustrated about the lens and the response by Pentax to your troubles.
I have some questions:
- What is the exact problem you have with the lens?
- Is the SDM too slower and/or slower than SD?
- Does low-light focusing work with SD but not with SDM?
- Are you worried that your lens is developing an SDM failure?
- What is your experience with the K-7 and your 16-50?
If your problem concerns focusing in low light, independently of SDM/SD and the camera body, then I'm sceptical Pentax can easily address this. You and others say the lens is great optically and I guess its focussing behaviour is part and parcel of that.
If I were you I would seriously test the K-7 and see how that helps the low light focusing with the 16-50. After all, the AF system is in the camera and while a lens can make it easier or harder for a body to achieve focus, a better body (i.e., K-7 instead of K20D) might just solve your problem.
Regarding SDM reliability: Somewhere I've read someone stating that the issue is with a connection within the lens which should have been designed more robustly, i.e. no problem with the technology as such. If that really is the case it shouldn't be that hard to address by Pentax and one can understand that they will probably do it behind the scenes and not publicly announce a "reliable SDM II".
Regarding SDM speed: There is this quandary between quick AF and precise AF / acceptable MF. Other manufacturers may have addressed this already but currently Pentax SDM seems to sacrifice speed in order to get the other advantages. My guess is it will take them a while to get a faster version of SDM since fast AF cannot be their priority given their position relative to Canikon.
Originally posted by Peter Zack The Tamron 17-50mm is having issues as well.
What issues? FF/BF?
I have no idea what the proportion of a potential 16-50 QC problem is and/or how unreliable SDM really is. I guess only Pentax and the repair centres have the numbers. It might be true that, when seeing the big picture, their is no real problem. But for a user who has a 100% trouble with the lens, it is no consolation that on a global scale the percentage of problems is acceptably low. I wished the responses by Pentax where more accommodating and their representation on the forum here is a very sad affair. Quite hard to believe actually. They must be doing well without extending their attention to (one of?) the largest Pentax user group.
I hope you get your trouble sorted soon.