I'm looking into a couple of lenses. I, however, being a 16 year-old highschool student have a fairly limited budget. Sigma, who i'm sure you've heard of, made/makes a series of lenses and filters for www.ritzcamera.com called Quantaray. I currently use a 28-80 nikon and a 70-300 nikon. I'd like to pick up a 28-300 and a super telephoto lens for sports and nature photography. This is the super telephoto i'm looking at; a 600-1000mm from quantaray: http://www.ritzcamera.com/product/251664843.htm For the 28-300, i was looking at this sigma over the nikon with the same range: http://www.sigma-photo.com/lenses/lenses_all_details.asp?id=3305&navigator=2 Any suggestions, opinions, experiences with sigma and quantaray? Good investments? Thanks in advance.