Hi. Please see the value of "Feather Radius".
For example, i make 2 layers. The lower is white (background) and the upper is black.
I make selection by - elliptical marquee tool (M) on the black layer and then right click on it. Choose the "Feather".
You will input what value you want.
For example i input 60. And i delete my selected area.
Yahooooo!!!! The result is what you see in this picture. You find it ok?