I have a vivitar 285HV and went to a football game recently. It was a night game in a poorly lit field. So I set my D2H with a 55-200mm to a shutter of 1/250 and a f/5.6. And My flash at full power. But every picture came out really underexposed. So is there some thing I'm doing wrong? Or should I get a SB-600 or something else?