The 40.5mm #47 Blue Filter from Tiffen is a filter designed to build contrast in black and white photography and creating separation between the tones. For landscape photography the filter will enhance haze and fog, which creates a more dramatic look. Skin tones are lightened for more detail and contrast control. Normally, the filter is intended for B&W photography, but can also be used in color photography to make special effects. The filter has a filter factor of 4.5, so you must increase by 2 1/3 of a stop for your exposure to compensate.