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 also available as standard in 0.1, 0.2, 0.3, 0.6, 0.9 and 1.2 with heavier densities available to order.
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 should be used for longer lenses. For extremely long focal lengths a razor edge grad providing a very highly defined transition, may be ordered.
Note: when ordering graduated filters in Panavision (4x5.65”) size, as these filters are not square, care should be taken to order either horizontal filters (i.e. landscape) or vertical (i.e. portrait) dependent on which way you will be using the filters in the matte box.
For more information, please see this
neutral density filters technical information PDF