The Heliopan 39mm Dark Yellow Filter is a basic contrast filter, primarily for use with black and white film, that very strongly darkens skies and blues, cuts through haze, increases contrast, and is often used for outdoor photography to emphasize contrast and shadows. Commonly used for landscape photography to emphasize blue skies and give clouds more visual depth. Also used for micro and infrared aerial photography applications where added contrast can be used to enhance detail. There is an approximate 4x filter factor with this filter, requiring an increase of 2 stops for normal exposure. NOTE: CHECK FILM MANUFACTURERS SPECIFICATIONS.