Neutral Density stands for neutral density. With the use of this X154 Neutral Gray ND2 filter, you can achieve a longer exposure time, then the film speed or sensitivity of the sensor of your camera would be allowed. Consider, for example, the recording of running water. This filter reduces the light with about three stops.
Cokin X-Pro series /sli Span>
The X-Pro series is aimed at professional photographers. You need an adapter ring and the Cokin filter holder for the X-Pro to attach this filter to your lens. The X-Pro series filters are recommended for use on lenses with a filter diameter between 62 mm and 112 mm.