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. NDs are also available in graduated filters, both in hard and soft edge. 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. Graduated NDs are available in Soft Edge or Hard Edge varieties. Soft edge grads have a smooth transition from clear to ND. 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 150mm Hard Edge filter is usable with Lee 150mm holders or any similar 150mm holder. The 0.6 filter reduces light by 2 Stops. This 150mm filter is usable with Lee 150mm holder systems or any similar 150mm holder. The filter is 150mm Wide but 170mm long to enable it to be easily moved up and down in the holder. The filter is also available in 85mm, 100mm and 165mm sizes.