Used primarily for black and white photography. Great for correcting skin tones, bringing out facial expressions in close-ups and emphasizing the feeling of liveliness. X1 is highly effective for indoor portraits under tungsten lighting. Filter Properties At A Glance Front Threads Yes Accepts Snap In Lens Cap Yes Filter Ring Depth (Less Threads) 5mm Coating Multi-Coated Filter Factor 2 Stops As their names suggests, these filters use HOYA colored glass. They are used for color correction of different light sources when using color film, or for controlling contrast with Black & White film. Color correction filters are important as color films do not have the flexibility of the human eye to automatically adjust to different situations. Black & White films register colors as shades of grey and the rendition of each color in a scene is important, so filters can be used to control this. The color of the glass used in all these filters is carefully controlled and to reduce the possibility of color shift over a period of time, such high quality filters are coated or multicoated on both sides. This maintains the desired effect and gives a long service life.