Separating an athlete from the background is one of the reasons I use the 400mm f/3.5 lens....the smallish, 1.5x or Nikon DX sensor size shows fairly deep depth of field even with a 200mm lens length,or even with a 300mm lens stopped down to say, f/5.6. But a 400mm focal length starts to make closer-range subjects stand out very much when placed in front of fairly distant backgrounds. This was shot on an uncomfortably hot,muggy,miserable day.