Thinking seriously about buying a used ef 28-70 f2.8l USM to replace my Sigma 24-70 f2.8 EX DG HSM. I've read that the 28-70 is sharper lens at all apertures & FL's than the ef 24-70, focuses as fast and is about $400 bucks less expensive, used. I'd be interested in some thoughts & feedback on this. My sigma is a very good lens as long as action isn't fast, but isn't fast enough in lower light situations when I'm trying to track action. There are times when I would like to have that versatile focal range in low light action. I'd love some feedback on this subject.


