http://www.adorama.com/SG1850PXAF.html
While Pentax sleeps, Sigma is bringing out an attractive line of lenses for DSLRs with APS-sized sensors. Pentax will wind up with less market share for lenses than they had before.
If Sigma were to bring out a high-quality 50-150/200 f2.8 or 4.0 constant aperture zoom I would probably buy it. I hope, though, that Pentax does it first.
Joe

