The Formatt-Hitech 4 x 5.65" Hard Edge Graduated Neutral Density 0.6 Glass Filter helps to specifically darken skies and other bright areas of the image. The filter is most dense at the edge and gradually lightens towards the middle, with a sharp transition line between the dense and transparent areas. By having only a portion of neutral density on the filter, you can selectively darken areas of an image whilst allowing the part of the image in the transparent section to receive normal exposure. Neutral density filters do not affect the colouration of the image and the density of 0.6 provides a 2 stop reduction of light entering the lens.nnFormatt-Hitech glass filters are manufactured from high quality Schott Superwite glass for exceptional clarity and maintained light transmission. This filter is compatible with the Formatt Hitech 100mm filter holder and measures 4 x 5.65" / 101.6 x 143.5mm. The horizontal orientation designation means that the transition line of this filter is parallel to the long side of the filter.nnn- 0.6 Hard Edge Graduated ND filter for darkening skies and other bright areas of the image.nn- Provides a 2 stop light reduction in selected areas.nn- Hard edge transition is ideal for circumstances where there is a clear, distinct separation line between the bright and dark areas of the image.nn- Neutral density filters do not affect the overall colouration of the image.nn- Compatible for use with the Formatt Hitech 100mm filter holder.