This 4 leaf trapezoidal barndoor set is specifically designed for use on the Profoto Magnum, Narrow Beam Reflector. Barndoors, Snoots, Grids, and Filters are essential accessories for any lighting system. These devices alter the shape, intensity, or color of the light output from your flash heads. Consider them as a painter would a brush, or a sculptor would a knife, or chisel. Use of a barndoor set will result in a shaft of light, when it is attached to the front of the reflector of your light source. The size of the shaft of light will be determined by the opening of the leaves, and the distance of the light from the subject. Rotating the barndoor set will determine the angle of the shaft of light. A 4-leaf barndoor provides more light control than a 2-leaf barndoor set.