This 150 x 170mm Hitech ND Blender Filter is a graduated neutral density filter providing a smooth dense to clear transition across the entire filter plane. This filter enables you to properly expose brighter areas of the image while compensating for darker areas. The subtle gradation from clear to maximum density means these filters do not have a hard separation line between the dense and clear areas, thus providing a more natural appearance and not requiring you to hide the grad line within the image.