The Tiffen 4 x 4" Blue 4 Hard Edge Graduated Filter is a hard-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.
Tiffen filters are 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. This filter measures 4 x 4" / 101.6 x 101.6mm.