Also known as a "didymium" filter, this is used to enhance red, orange and brown subjects to give more color saturation and contrast, while having very little effect on other colors. It can be used in many situations such as architecture where certain building features need emphasizing, or for landscapes to enhance foliage and rocky features.
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.