Cokin graduated gray ND filters are part clear, part neutral density. They allow the transition to be blended into the scene, often imperceptibly. A ND.6-to-clear, with a two stop differential, will generally compensate the average bright sky-to-foreground situation and is also the most popular density of the series.
The Z-PRO Series is recommended for focal lengths of 20mm and onwards (in the 35mm format). This filter is made of CR39 Resin which is a reputable lightweight and unbreakable optical material also used for ophtalmic glasses.
Please Note: This filter measures 100 x 150mm (4" x 6") and fits the Cokin Z-Pro filter holder