Originally posted by seventysixersfan Assuming you mean sigma 17-50mm, it's excellent but a bit bulky. I used to have the old sigma 18-50 (first version, 445 grams, 67mm filter size) which was okay but not stellar. The second version of the 18-50 had "macro" in the name and weighed about the same though has a larger 72mm filter. I later got a sigma 17-50 (565 grams, 77mm filter size) which was outstanding, quiet focusing (HSM motor), and performed optically very well on my KP. Used the largest KP grip, and even better to use the battery grip attachment.
I too have this Sigma 17-50mm f/2.8 EX DC HSM, use in on my KP and it is indeed just as good as described here^. I prefer using the largest supplied grip with it, and with the great matchup- a DA* 50-135mm f/2.8 as well. The f/2.8 aperture throughout is a major advantage, with a brighter VF and superior shutter speed especially for low light use. That said, my DA 20-40mm Ltd is also a fine pairing with this DA* tele-zoom, when f/4 is good enough for the need, and the reduced FL range is good enough also. It is more compact, very well-built, and offers WR throughout.
Worth noting, a new Pentax DA* 16-50mm f/2.8 PLM lens with top-flight WR construction is due to arrive soon, but will no doubt cost a whole lot more.