"81" series are color corrective filters that 'warm' bluish tones. They are available in several strengths (A, B, C & EF) with 'A' being the mildest warming effect. Adds healthy tone to skin tones shot in open shade or overcast. Reduces excess blue from flash indoors or in daylight flash-fill. Warms (balances) sea, sky and high altitude shots. Multi coated for flare prevention.