Sigma 18-200mm f/3.5-6.3 DC Lens for Pentax ...- User Rating: 



Summary for Sigma 18-200mm f/3.5-6.3 DC Lens for Pentax ...- Garbage - wait for Pentax
Notes on Sigma 18-200mm f/3.5-6.3 DC Lens for Pentax ...- This is the worst camera lens I've ever had the misfortune to use.
I wanted something I could travel with to replace my 18-55mm kit lens (I have a K100D) plus the 50-200mm telephoto zoom. These are great lenses but I was trying to hold down the bulk and weight, so I gave Sigma a try.
Big mistake. This thing is TERRIBLE. Horrible chromatic distortion -- I frequently got BOTH purple and green fringing effects on opposite sides. Depending on the zoom and the angle I was shooting at, I got laughably distorted barrel and pincushioning -- sometimes in THE SAME SHOT. Literally, the extreme barrel distortion would flare back out at the corners. And it won't focus properly -- the center will be fairly crisp but the edges will be completely gone -- not the far edges either, but a mere third of the way across the frame. It vignettes really badly.
This is a CRAPPY, CRAPPY lens. I've seen better on dollar trashcams in the thrift store.