Well I purchased the Sigma 17-70mm to go with my lovely new K7D about 2 and a half weeks ago.
First lense I found was having trouble get sharp auto focus, many of my images were coming out somewhat soft.
I swapped it over a couple of days later for another one which seemed to giving me sharper results than the first. I kept it for 2 weeks and in general liked the lense, good zoom range, macroperformance and speed, however I was finding that the colours from it were a tad dull and photos only seemed to pop after post processing, which is fair enough.
In the last few days I found my lense started developing an ANNOYING zoom creep making it unusable. Even if tilted as little as 45' the lense would creep substantially, for example so much as having the lense at around 20mm it'd either extended all the way out to 70mm or drop back to 17mm, very frustrating.
So today I just paid extra and swapped it over for a Pentax 16-45mm, so far I'm a lot happier, seems to autofocus faster, images are sharper.
Only thing I miss is the extra zoom, speed and macro performance of the Sigma however I really love the feel and the performance of the Pentax so far.
Last edited by Christopher M.W.T; 07-27-2009 at 01:24 AM.