Excerpt: This product is superb in optics but flawed in some areas. That being said, it doesn't mean you should blame the lens for it's flaws. This is a lens that need a lot of time to get familiarised with its functions and how to maximise its output. For example, on some Pentax body the auto-focus will hunt or fail under low-light (which lens doesn't?) So you need time to know when the lens will work and when it won't, otherwise you will not be able to get good results from it.
Pros: Large Constant Aperture, Nice Bokeh, Strong Construction, Weather resistant
Excerpt: Excellent, fast normal zoom, with great build quality. I've been considering this lens for sometime but already own the Tamron non-vc 17-50mm f2.8. I was hesistant to buy the DA* with all the SDM issues reported online. However, after a good experience with the DA* 50-135, finally decided to give this lens a try. Compared to the Tamron - Better colors, contrast, slightly brighter, better build quality, weatherproof and silent.
Pros: Consistent Output, Fast / accurate auto-focus, Nice Bokeh, Rugged, Strong Construction
Excerpt: I bought this lens in the May of 2012, it was used. And I bought it for my brother, who is also Pentaxian. Because he has Me as his elder Bro. Before making this purchase I already had FA 16-45 and Kit lens and some others, so I had an alternative and also tried and was looking after other Third party lenses, and actually was thinking about Sigma as a better choice.
Summary: I needed a weather-resistant wide-angle for my K-5, and certainly got it. It features a fast, quiet autofocus, and takes sharp, well-coloured images. On the downside, it's pretty heavy, and a little hard on the pocketbook. I bought it because I needed the weather sealing, but if that's not an issue to you, a third-party lens might serve you just as well, for a fraction of the coin.
Excerpt: The good news is that with the new k5iis there is an improve in focus speed. It is now comparable to 18-135 testing them one after another. Ca @ f2.8 has also reduced using the new body. Overall sharpness increased as well.