Increases contrast between reds and yellows. Particularly useful for distant outdoor shots taken with a telephoto lens. Also useful in color photography for spectacular sunsets, seascapes, etc.
FOR COLOR FILM:
These filters, such as K2 (Yellow), G (Orange), 25A (Red), and X1 (Green) are primarily designed for use with Black & White film. However, they can be used with color film to produce special color effects.