I am looking at an ND grad filter for some of my landscape shots. I don't know much about filters so tell me if I'm way off base here. As I understand the ND grad filter can be used to help expose two different parts of a scene properly. I mean lets say you have a bright sky and to expose for it properly would underexpose the foreground. By placing the filter appropriately you could properly expose for the ground and the sky, or at least get closer. Is that about right?