The Tiffen 49mm Black & White Three Filter Kit combines the essential yellow #6, green #13, and red #25 contrast filters together, along with a four-pocket filter pouch, to provide a convenient solution for producing varying degrees of contrast when working with black and white film. Tiffen filters are made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass, grinding flat to a tolerance of 10,000th of an inch, and then mounting to precision metal rings. Tiffen 49mm #13 (2) Green Filter The Tiffen 49mm #13 (2) Green Filter is a basic contrast filter, primarily for use with black and white film. This green filter subtly darkens skies and lightens foliage. It is commonly associated for use with portraiture and attaining greater separation from skin tones and outdoor backgrounds. When compared to the #11 yellow-green filter, the #13 helps to lighten foliage and other green-colored subjects more. There is a 2x filter factor with this filter, requiring an increase of 1 stop for normal exposure. Tiffen filters are made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass, grinding flat to a tolerance of 10,000th of an inch, and then mounting to precision metal rings. Green contrast filter for black and white film subtly darkens skies and lightens foliage. Suited for portraiture, this filter helps to separate skin tones from outdoor backgrounds. Tiffen filters are made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass, grinding flat to a tolerance of 10,000th of an inch, and then mounting to precision metal rings. Tiffen #25 Red Filter (49mm) The 49mm #25 Red Filter from Tiffen is a filter designed to build contrast in black and white photography and creates separation between the tones. Using this filter it creates dramatic skies or simulate a moonlit scene during the day.