The 77mm Peter McKinnon Signature Edition Variable ND 0.6 to 1.5 Filter from PolarPro is designed to mount onto lenses with 77mm front filter threads and provides an exposure reduction of 2 to 5 stops. The 0.6 to 1.5 density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than usually possible.