The Cokin E2 Hard-Edge Graduated Emerald is a 3-stop emerald that filter can be used to enhance dull, flat, or hazy skies. The filter is densest at the edge and graduates to clear at the middle, with a hard-edged line of transition. Hard-edge filters are great for images with a defined horizon line. The filter is rectangle so you can selectively choose where the emerald edge sits in the framing of the image.