The Tiffen 6.6 x 6.6" 3 Cool Blue Hard-Edge Graduated Filter helps to specifically add a cool, purplish-blue coloration to skies and other bright areas of an image while allowing a portion of the image to remain neutrally colored. The filters coloring is densest at the edge and tapers to clear by the middle, with a hard-edged transition between the density and clear areas. The 3 color density provides less cool blue coloration than the 4 density, but more than the 2 density filter. This filter is made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass and grinding flat to a tolerance of 1/10,000th of an inch. It measures 6.6 x 6.6" / 167.6 x 167.6mm. Provides a deep cool blue coloring to select areas of the image. 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.