Summary: I like using this lens for all the times my family is sitting at the kitchen table or playing in the living room. It enables me to go without flash most of the time in those situations. However, it is also a very fine lens for those times when I want to be a "serious hobbyist." It does macro as well as a dedicated 1:1 macro lens that I recently owned. I also own a sigma 50-150 and it is also very nice. Together the 2 cover the field for me.
Summary: Lens is fast and images are rendered sharp. Bokeh at f4 is just awesome. HSM motor really delivers and its quiet, really quiet. Love the weight on the lens and it sits proudly on my kx unit. Would recommend this lens to anyone who is looking for a good short tele range.
Summary: The Sigma 70mm f2.8 DG EX macro is among the best 4 best macro lenses in the world: Canon 100mm f2.8L IS, Nikon 105mm f2.8 VR Micro and probably the sharpest one Sigma 150 f2.8 DG EX macro. Sigma 70mm f2.8 EX DG (special color corrected multi-coating and designed for any format APS or full-frame sensors) is absolutely sharp with great "bokeh" for macro shots and also portraits (sometimes too sharp for portraits).
Summary: This is currently my favorite lens. Echoing the other reviewers, the range is perfect for a walkaround lens and a perfect sub for the kit lens. Solid construction; it's got some weight to it. Smooth focusing, and sharp images. Macro to boot (see photos I've posted). If you don't have a lens in the 17-70 range or are thinking of upgrading from the kit lens, you should consider investing in this. You'll get your money's worth.
Summary: Best bang for the buck walkaround lens for my K-r. Had the Tamron 17-50 F2.8, but lacked the reach. The Sigma, while lacking 2.8 across its FL (but, mind you, you're not paying the exorbinant $$ that would bring), does have 2.8 at the wide end, has the 70mm reach that gives that extra that kit lens lack. Optically, my copy is sharp, no focusing issues. Colors are rendered vibrantly, sharp in the corners, solidly built....I'm pleased...
Summary: I purchased this lens to replace the standard kit lens that came with the Pentax K10D. It has proven to be of exceptional quality both optically and mechanically. I have shot it under many varied situations and it continues to give me the exact results I hoped for. I plan to purchase the Sigma 70~300 APO MAcro zoom soon to supplement the 17~70 and expect the combo to fit 99% of my lens needs.
Summary: I purchased this lens for my Pentax K10D, and it works quite well. The zoom range is just right for most applications and the semi macro performance is handy. Performance wise it is very sharp, low CA, low vignetting and low distortions. At 17mm the performance sags a little with some distortion and when wide open some vignetting. In most cases I haven't had a problem.