ND Filters are all about holding back light to give you a slow shutter speed.
As seen is this video by Mike Browne – an ND 1000 (big stopper) filter has the effect of allowing anything that is moving in your image to become blurred or ghost like, for example clouds, waterfalls, rivers and the sea.
If you find this video useful then be sure to check out more from Mike Browne on ND Filters.
If you are looking to buy ND filters and kit then look no further than SRB Photographic, where I bought mine from. 😉