The Urth 77mm Soft Graduated ND8 Lens Filter Plus+ is a graduated grey filter that provides a fixed light reduction of 3 stops in the darkest part. Graduated ND filters are designed with a gradient from light to dark, with one end being completely transparent and the other end darker. By placing the filter in front of the lens, you can darken a specific part of the image (usually the lighter part) without affecting the rest of the image. This helps achieve balanced exposure between the bright sky and the dark foreground in landscape photography, for example.