Exclusive Hoya ACCU-ND technology ensures accurate color balance when switching between ProND filters Filter provides "X" amount of neutral density stops (depending on the filter you can insert X-see press release) Manufactured from super high quality "Hoya Clear" optical glass Assembled using a one-piece aluminum frame creating a rigid, durable, but lightweight filter Perfect for Still and Video applications The ACCU-ND technology in the Hoya PROND filters yields a truly neutral color balance that will not add any noticeable color-cast to your images. The Hoya PROND series is aimed at the still photography and HDSLR video markets. The series provides 9 filters from two stop to 10 stop light reduction. The Metallic ACCU-ND coating on the PROND filters do not color shift as you move from one density to the next, a common problem with other series of neutral density filters. Now you can set your white balance once and have the same color balance even if you need to change filters due to changes in lighting, or for creative effect. The PROND filters use Hoya's exclusive clear optical glass that has a metallic ACCU-ND coating front and back to create the neutral density affect. Neutral density filters are designed to reduce the amount of light entering your camera lens and should not have any other effect on the image. Reducing the amount of light allows for the use of wider apertures or slower shutter speeds for creative and dramatic effect in bright lighting conditions. All Hoya PROND filters have a low-profile one piece aluminum frame. The thin frame keeps the glass secure and parallel to the sensor while allowing it to be used with super-wide angle lenses.