B+W 52mm BASIC Graduated Neutral Density 701M (50%, 1 stop) Filter, darkens the subject area by one f-stop without changing its color. Ideal for Landscape Photography, the 701M is finely polished glass and lasts longer than easily scratchable plastic substrates. It is used to compensate for a sky that is too bright compared to a dark foreground, and has a rotatable mount for precise horizontal alignment.