The Tiffen 4 x 4" Combination 81EF/ND 0.9 Filter blends both an amber light-balancing 81EF and a 0.9 neutral density filter. The ND filtration provides a 3-stop exposure reduction for darkening the entire image in order to photograph with a wider aperture or slower shutter speed than normally required. The 81EF filtration covers the entire filter plane and lessens the color temperature by 650K, enabling the ability to attain 3200K balance when the prevailing light source is 3850K.
This filter is made using ColorCore technology, a process that involves laminating the filter substrate between two 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.