Tiffen 6.6x6.6" Water White Glass Soft Edge Graduated ND Filter, 0.9 (3 Stops)

Often, you want to balance light intensity between two areas within a scene. This is important outdoors to allow more sky detail while properly exposing the foreground. Exposing for the foreground will produce a washed-out, over-exposed sky, exposing for the sky will leave the foreground dark, underexposed.