The ND Grad Hard Edge Kit contains the most commonly used densities of the Hard Edge Neutral Density filter - 0.3 (1stop), 0.6 (2 stops) and 0.9 (3 stops). Neutral density (or ND) filters produce a grey neutral tone and are used in photography to reduce light, enabling more control over exposure and depth of field without affecting color contrast. These filters are clear in the bottom half of the filter with a gradual transition to the ND effect in the top half. They are primarily used for light reduction in skylines of landscape shots. Hard edge grads have a more defined hard lined transition and are usually used for longer focal lengths. ND Grads are made in different densities according to the level of light reduction from 1/3 to as much as 4 stops of light. This 100mm filter kit is usable with Formatt-Hitech 100mm holder systems or any 100mm holder. The filters in this kit are 100mm wide but 150mm long to enable easy movement up and down in the holder.