Made out of high-quality optical glass, the Lee 150x150mm SW150 Mark II Little Stopper is a long-exposure ND filter designed to reduce the amount of light entering the lens by up to 6 f-stops. The Little Stopper is ideal for low-light conditions at the beginning and end of the day (when the Big Stopper's ten stops may prove too much), allowing you to enjoy increased flexibility with exposure lengths. By increasing the length of exposure time, the Little Stopper adds a ghostly, time-passing effect of anything that moves (E.G. sea, clouds, waterfalls, people etc.). The Lilttle Stopper is compatible with the Lee SW150 Mark II Filter System (not included).