This kit contains a Cokin Z-Pro Filter Holder plus:
#121L Graduated Light Gray G2 Filter
#121M Graduated Medium Gray G2 Filter
#121S Graduated Soft Gray G2 Filter
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.
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 onwards (in the 35mm format).