Compatible with Lee's SW-150 series filter holder system, this Neutral Density Graduated Hard filter set contains a 0.3 (1 stop), 0.6 (2 stop) and 0.9 (3 stop). ND grads are primarily used by landscape photographers, as they allow users to adjust exposure and darken specific areas of an image without affecting the colour balance, such as an over exposed sky, while keeping the rest of the foreground correctly exposed. Each filter features a hard transition from light to dark and measure 150 x 170mm.