Made out of high-quality optical glass, the Lee 150x150mm SW150 Mark II Big Stopper Filter is a long-exposure ND filter designed to reduce the amount of light entering the lens by up to 10 f-stops. Compatible with the SW150 Mark II System, the Big Stopper is aimed at landscape photographers who use ultra-wide-angle lenses. By greatly extending exposure times the Big Stopper has the effect of allowing anything that is moving in your image to become blurred or ghost-like (e.g. clouds, water etc.). However, the effect is not limited to landscapes and can also be used on cityscapes to blur moving people or cars. The Big Stopper is compatible with the Lee SW150 Filter Holder (not included).