The Heliopan 77mm Variable Gray ND Filter is a solid variable neutral density filter providing a reduction of about 1 to 6 stops. The 0.3 to 1.8 density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally required. The degree of density is easily controlled by rotating the front filter ring, allowing you to previsualize the additional exposure length required. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily. Neutral density filters do not affect the coloration of the image. This filter features a brass mounting ring that is painted matte black to help reduce reflections. High quality Schott glass provides optical clarity and greater contrast to help render scenes with greater fidelity and resolution. This filter does not have front threads for attaching other filters.