The cokin a series a037 warm 81ef filter is designed to add warmth to a photograph whilst removing bluish casts from open shades this filter controls bluish coronation found in daylight film as well as eliminates excessive amounts of blue from the effects of electronic flashes it is also stronger than the 81a 81b 81c and 81d this product is a mild light balancing filter which reduces colour temperature slightly for a warmer tone it corrects propensity towards blue tones and alters c