One half of this filter is NDx4 Neutral Density and the other half is clear, with a soft boundary between the two. It is used to control bright/dark contrast, by reducing half the shot by 2 stops. Particularly useful in landscape photography, the rotating mount allows bright skies to be easily controlled for dramatic effect.
In order to avoid purchasing one of those counterfeit filters we highly recommend to purchase only from official retailers that are recognized by HOYA's official global distributors. Prior the purchase kindly inquire and verify whether a retailer is authorized by HOYA global distributors. You may find the contact in the HOYA global distributors list.