Hoya HD3 lens filters claim to be 4x stronger than optical glass: Digital Photography Review
Hoya HD MARK II CIRCULAR-POLAR 52mm szűrő | Hoya HD MARK II CIRCULAR-POLAR szűrők | Filters | Lenses and Accessories | Products | Camera - Canon, Nikon, Pentax | Photo printing | Fotoplus
Amazon.com : Hoya 52mm Variable Density Screw-in Filter : Camera Lens Neutral Density Filters : Electronics