This Tiffen 4x5.65" Soft Edge Graduated 0.6 Filter (Horizontal Orientation) is a two stop graduated ND filter that reduces exposure on top of your frame, helping darkening skies since it's the densest at the top of the frame. It is called "soft-edge" because it tapes to clear with a soft-edged line of transition. If you are looking for a more subtle darkening of the top of your frame, you should use the one-stop graduated ND.