I will be shooting some high school football next year. Can I get some idea of what works in terms of a lens? I have a D50 and no telephoto lenses (well I do have a 85 1.8). What is the minimum aperture...I am assuming 2.8. What about focal lengh...200, 300, more? I have been looking at 80-200 2.8, 70-200 2.8, and 70-300 VR. Thanks.