[davidmanze]

I also had some troubles with the Tamron 17-50 on Pentax and the lens travelled more than me by sending it from Switzerland to Tamron Germany. Twice, once with the body. At that time I wasn't used to the shipping costs 

 

Thanks for reminding me, dave's clichés how much easier my life is since i abandoned the Pentax boat. On the other side, at the time I had some Pentax and Sigma lenses I had not idea what happens if a lens is decenterred. And am pretty sure, I wouldn't have been able to recognize one. Anyway, I was pretty happy with my 4 Sigmas at that time.

 

Talking of moving elements of lenses: I always remained sceptical to Pentax' inbuilt vibration reduction - a moving sensor brings another variable into the game. What, if the motors or electronics is a bit faulty? Trying to compensate shutter vibration can fail.

 

I've been happy with the SR system from the Pentax K5, with one caveat, you must wait until the green hand is alight, other than that it's good and "very reliable" and there's no glass elements moving around. The AF is it's Achilles heel, but even that is decent enough once you get the hang of it. 

      Now I have martyred my way through those decentered lenses and have a good range of glass from 8mm fisheye  through to the 50-500 Sigma , I will live with it for years, not going through that again in another mount.

    It will be a K3 soon for the extra resolution and better AF, one thing you can say about Pentax is it's handling, ruggedness and compact size, if I can't get decent photos out of that lot it's me that's no good not the gear!. 

  If I was starting over again I would have gone Nikon.