The Formatt 4x4" Hi Def Clear Glass Filter is a clear (colorless) filter for color and black-and-white film. It also serves as permanent protection for the lens.nnHi Def Filtersnn- Hi Def filters do not suffer from color shift - Specially designed for use with high-definition shootingn- Optically consistent from one filter to anothern- Formatt filters use the finest materials combined with cutting-edge production techniques, achieving a level of optical perfection unmatched elsewheren- All Formatt filters are manufactured with Schott-Desag B270 Crown optical glass, precision polished and ground to guarantee absolute optical flatness and optimal performancennAbsorbent Cell Technologynn- The secret to Formatt's consistency in filter design lies in its unique “Absorbent Cell Technology” (A.C.T.); This unique process allows color-true dyes to be applied to optically pure, ultra-thin absorbent cells, providing control that ensures the smoothest gradient lines and consistent color across the entire filter surface.nn- This process is revolutionary compared to conventional filter dyeing techniques, as it eliminates the need to coat the glass surface directly; The reproducible performance achieved through A.C.T. ensures that at any time, you can confidently swap similar filters without perceptible differences in color or density.nn- The flatness of each filter is guaranteed to a maximum of 2 waves and is accompanied by an individual measurement performed by a laser interferometer; Each filter is carefully checked using a densitometer and spectrophotometer to ensure consistent and accurate transmission before leaving the factory - the result is absolute image purity that eliminates any unwanted color cast caused by conventional greenish soda-lime glass.nnUltraviolet Filtersnn- If desired, they can be left permanently on the lens for protectionn- Haze filters offer additional correction benefits for ultraviolet (UV) light that can register on film and videotape as a bluish cast and can obscure distant detailsn- Ultraviolet filters allow you to correct the UV effect to varying degrees