Often it is necessary or desirable to balance the light intensity in one part of a scene with another. This is especially true in situations where you don't have total light control, as in bright contrasty landscapes. Exposing for the foreground will produce a washed-out, over-exposed sky while exposing for the sky will leave the foreground dark and under-exposed.
Lee graduated gray ND filters are part clear, part neutral density. They allow the transition to be blended into the scene, often imperceptibly. A ND 0.75-to-clear, with a two and half stop differential, will generally compensate the average bright sky-to-foreground situation and is also the most popular density of the series.
Lee graduated resin filters are 100 × 150 mm and 2 mm thick. The 150 mm length allows for adjustment of the filter within the holder.