The Cokin B2 Soft-Edge Graduated Blue is a 1 2/3-stop blue filter that 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 soft-edged line of transition. Soft-edge filters are great for images with an undefined horizon line like mountains or cityscapes. The filter is rectangle so you can selectively choose where the blue edge sits in the framing of the image.