The design of gradual decrease of transparency towards the center of the filter allows an emphasis of foregrounds or backgrounds, therefore the boundary between the colored and transparent sections of lens will not become apparent. This filter is mounted on a rotating frame, so you will be able to rotate the coloring at any part of your image. It gives your landscape and skin texture a more colorful touch. Material: 1.5mm Optical Glass, Black Rimmed Frame (Thickness): 6.5 mm