I'm continuing in my efforts to learn as much as possible about my Nikon D5100 and I had a really quick question. For portrait purposes, regardless of focal length, if both are set to the same aperture then you will be getting the exact same amount of light. What I was curious about is why would you use a 300mm f/2.8 versus say a 50mm f/2.8? Does one allow for more blurring of the background? I mean I could understand if flash was being used then being further away from your subject might help reduce the harshness of light, but if no flash is used then what is the advantage of one focal length versus the other? Thanks everyone!