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. ND Grads 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. They are made in different densities according to the level of light reduction from 1 stop to 4 stops of light. Formatt-Hitech filters are made from the highest quality 1.5mm optical resin.