The 77mm Peter McKinnon Edition Variable Neutral Density 1.8 to 2.7 Filter from PolarPro is designed to mount onto lenses with 77mm front filter threads and provides an exposure reduction of 6 to 9 stops. The 1.8 to 2.7 density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than usually possible. The degree of density is easily controlled by rotating the front filter ring, helping you to predetermine 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. For easier, repeatable control over density settings, the front ring is visually demarcated with numbers representing the different stop values and features side knurlings to further enable fast and precise positioning. To help ensure consistent exposures, the front ring is designed to prevent any rotation beyond the stop values etched on it.