https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/231642-tried-out-da-16-50-a.html
A few years ago at EXPOsure, I went to the Pentax booth... and did a similar trial to the one above... I used my the 16-50, 15 ltd and my 10-17 fisheye set to 15mmm, to compare images....the image from the 16-50 was my least favourite of the group. In the end, we bought a Sigma 8-16 and a Tamron 17-50, if I'm going to pay for a DA*16-50 it's going to have to show me a little more than it did that day. Most of us have little time for these types of comparisons so even though I'm sure the nay sayers will say I didn't give it a fair shot... I gave it what i could afford, and I wasn't impressed. Given that it is most likely the least reliable lens Pentax has ever produced or ever produced for a Pentax by any company it's even more problematic. The two lenses I did get are both keepers. We barely use the Tamron 17-50 2.8, but for the images we get when we do use it, it's worth keeping it on the shelf most of the time and hauling it out when needed. The Sigma 8-16, just continues to amaze. Weather sealing is important to me... but IQ is more important and price is always, a factor.