The Cokin 1-stop neutral Density filter is a solid ND filter providing 1-stop exposure reduction. This creates an overall darkening of the image, allowing you to photograph with a wider aperture or slower shutter speed than current lighting conditions allow. Slowing your exposure time lets you convey movement in subjects like water and clouds. Increasing your aperture lets you create a shallower depth-of-field which isolates your subject from the background. Neutral Density filters do not affect Color and can be combined with other filters to create more dramatic effects.
Cokin filters were invented by professional photographer Jean Coquin. By using square filters like Cokins, which fit into a holder and are attached to a lens via an adapter ring, the photographer has a number of immediate advantages. There is no need to duplicate filters to fit different size lenses, up to three filters can be used at once to create unique effects, and the photographer has control over the positioning of the effect on the photograph.