The Tiffen 6 x 6" Blue 4 Soft Edge Graduated Filter is a soft-edged graduated color filter providing a bluish color across the image, giving a cooling effect for your photographs. The graduated filter design keeps a portion of the image neutral, resulting in a more realistic look while allowing for the sky or other bright areas to take on the color of the density. The 4 density provides less of a blue cast than the 5 density filter, but more than the 3 density.