ND filters (Neutral Density) reduce the amount of light reaching the film without affecting the color. Can be used to enable slower shutter speeds. Also can be used to better separate subjects from the background by allowing wider apertures, effectively decreasing depth of field. Great for portraiture and outdoor scenes.
Simply mount the adapter ring and filter holder (sold separately) to the front of your lens, then slide in different filters to take beautiful, colorful shots. Combine different filters to obtain a wide variety of colors.
ND filters are one of the least expensive and most effective ways to dramatically improve your shots.