The Kodak 3 x 3" #25 Red Wratten Gel Filter for Tricolor/Color Separation Work is ideal for strong contrast improvement, since it absorbs green and blue completely, and enhances red.
Clouds are dramatically improved, almost to the mood of a thunderstorm. It is more effective in cutting through haze, and moonlight effects are easily accomplished. It is also suited for infrared photography.
Most Kodak gelatin filters are available in 3 x 3" (75 x 75mm), 4 x 4" (100 x 100mm), 6 x 6" (150 x 150mm), 14 x 18" (350 x 450mm) and 4 x 12" (10.2 x 30.5cm).
