Please help - I am looking for a decent wide angle zoom (@ 25-75mm) with a constant f/2.8 (for indoor sports) that is not alot of money. I am a mom with photography as a hobby, nowhere near an expert, and am looking for this lens to take pics of basketball and volleyball. I currently have the NIKKOR 50mm f/1.8 and love it but feel limited with the focal length. I can't afford the NIKKOR lenses in this range so am looking for suggestions. I've been looking at the SIGMA 28-70mm f/2.8 EX DG and the Tamron 28-75mm f/2.8 SP XR. Any comparisons on these lenses or other suggestions? Also, I know the f/2.8 vs my current 1.8 will make a difference but will I still be able to get at least some good shots? Thanks for any help.