The Formatt Hi Def 5.65 x 5.65" Clear Glass Filter is a clear (colourless) filter for colour and black and white film. It also serves as permanent protection for the lens.nnnHi Def Filtersnn- Hi Def filters undergo no colour change - Specially designed for High Definition shootingn- Optically consistent from one filter to anothern- Formatt filters use the finest materials combined with state-of-the-art production techniques; this has resulted in a level of optical perfection unmatched elsewheren- All Formatt filters are manufactured with Schott-Desag B270 Crown optical glass, precisely polished and ground to ensure absolute optical flatness and optimal optical performancennnAbsorbent Cell Technologynn- The secret to Formatt's consistency in filter design lies in its unique "Absorbent Cell Technology" (A.C.T.); this unique process enables colour-matched dyes to be applied to optically pure, ultra-thin absorbent cells, providing control that ensures the smoothest gradient lines and homogeneous colour 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 during shooting, without perceptible differences in colour or density.nn- Each filter's flatness is guaranteed to a maximum value of 2 waves and is accompanied by an individual measurement from a laser interferometer; each filter is carefully verified with a densitometer and spectrophotometer to ensure consistent and accurate transmission before leaving the factory - the result is absolute image purity that eliminates any unwanted colour cast caused by conventional greenish soda-lime glass.nnnUltraviolet Filtersnn- If desired, they can be left permanently on the lens for protectionnn- Anti-haze filters offer additional correction benefits for ultraviolet (UV) light which can register on film and videotape as a bluish cast and can mask distant detailsnn- Ultraviolet filters allow you to correct the UV effect to varying degrees