Some high-contrast scenes are difficult for many lenses, not just the cheaper ones. A tree branch against the sky is a classic example. Don't be afraid to stop it down to f/16 if necessary, esp. at the long end of your lens. You could also try manual focus if your AF is hunting quite a bit. I've heard good things about Faststone, but dont have much experience with it. Most of the commercial image editors will have PF tools. For a freeware solution, the GIMP has a couple of PF scripts - this one works pretty well:
Fixing Purple Fringing and Chromatic Aberration with Darla's GIMP Scripts for Digital Photographs
Last edited by paulh; 12-02-2011 at 02:53 PM.