Hello, I'm looking to buy a faster zoom to mainly be used on the *istD. I have the DA 16-45 4.0 already. At times this zoom is too slow. It cannot focus on dark objects outside in low light situations (cloudy) at times. Most of the time it's no big deal to manually focus, however, their are times when I do not have the time to manually focus in order to get the shot.
I have been looking at a couple of Sigma zooms. The 18-50 2.8 EX DC (digital only), and the 17-35 2.8-4.0 EX DG. The latter is slower, however, will work good with either a digital or my analog Pentax bodies. I was hoping some people would have experience with these zooms and offer up comments. Thanks, Chad
