Rodenstock Neutral Density filters, reduce all visible colors equally, e.g. by two f-stops. This allows motion blur to be achieved with a longer exposure time than would otherwise be permitted by the brightness of the illumination and the film speed or sensor sensitivity. They also provides less depth of field with a larger aperture . Another application is the light reduction in situations where the brightness is too high for a correct exposure with the shortest exposure time available at the given film speed or sensor sensitivity. As the effect of ND filters cannot be replaced by digital imaging software at a later date, these filters offer many advantages for digital photography