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. These filters are double threaded allowing additional filters or accessories to be mounted one over the other. Made of high quality plastic and aluminum metal. Multicoated lens for reduced lens flare and ghosting caused by reflections. Filters serve as a great and inexpensive lens protector. Use one at all times to protect your delicate lens from dirt, scratches and accidental damage. Better to scratch or break a filter than an expensive lens.