Neutral Density filters evenly reduce the amount of light passing thru the lens without effecting color. Ideal for reducing bright light in large aperature situations when a narrow depth is field is needed. Allows for slower shutter speeds when blurring or showing of movement is desired. Allows balancing of exposure to highlight a key subject. Lets you use higher speed films in bright light. Hoya Neutral Density filters are available in most sizes and in three strengths:.3 (2x) Reduces the light one f-stop.6 (4x) Reduces the light two f-stops.9 (8x) Reduces the light three f-stops.