The 81 Series of filters controls the bluish coloration that can affect daylight film. They warm scenes shot on cloudy days. They can also remove excessive blue from the effects of electronic flash. These filters are also good for general scenics when the photographer wishes to remove the bluish cast from open shade or just add warmth to the photograph. The 81 series is available in grades from 81 through 81EF , with 81EF having the warmest effect.
Optiflex resin filters are made from durable, lightweight, optical resin and are slightly thicker than standard gelatin filters. These filters are available in 3 x 3" (75 x 75mm) and 4 x 4" (100 x 100mm) and are 0.4mm thick.
81 Series Color Conversion Chart
81 decreases color temperature 100 degrees Kelvin
81A decreases color temperature 200 degrees Kelvin
81B decreases color temperature 300 degrees Kelvin
81C decreases color temperature 400 degrees Kelvin
81D decreases color temperature 500 degrees Kelvin
81EF decreases color temperature 700 degrees Kelvin