Originally posted by VoiceOfReason The Pentax lens that would fit be the closest competitor to the Sigma 17-50 f/2.8 or the Tamron 17-50 f/2.8 is the Pentax DA* 16-50 f/2.8. It's the only one that is weather resistant of the three, and it has an extra 1mm on the wide end. That being said I went with the Tamron myself. Of course if you REALLY want wide and don't mind a slower lens there is the Pentax 12-24 (PITA to get), Pentax 10-17 fisheye, Tamron 10-24 (great lens BTW), 2 versions of the Sigma 10-20, and then, if you REALLY want wide the Sigma 8-16 (great lens).
I read a review on here of the 3 17-50 and I believe that pentax came in last. The smaller focal length lens would be nice but I don't think I would use them as often and I would be swaping lens more often.