The Heliopan Series 7 Dark Red Filter is a basic contrast filter, primarily for use with black and white film, that completely absorbs blue and green tones, enhances reds, cuts through haze, and increases contrast for outdoor photography. It is suitable for use in tri-color separations and for photographing faded documents. There is an approximate 8-12x filter factor with this filter, requiring an increase of 3 to 3.5 stops for normal exposure. Same as (25) except with a more pronounced effect.