The 80 series of filters are blue. They are used to balance daylight film under artificial, tungsten or standard (household) incandescent lighting.
Let's say you're at a family gathering and you've brought your camera and want to take some photos of this once-a-year gathering. You have traditional daylight balanced film but find yourself in a room filled with table lamps. If left unfiltered, your photos will turn out yellowish. Under certain circumstances, perhaps a nice effect but not flattering in terms of skin tones or what our eyes are used to seeing or expecting. Enter the 80A filter!...
This filter allows you to "balance", i.e. bring back, correct color tone to your images. There is some loss of film speed that may require the use of a tripod but, at least, your photos will demonstrate the proper tonality they so richly deserve.
80 Series Color Conversion Chart
80A increases color temperature from 3200-5500 degrees Kelvin (commonly used with 3200K lamps)
80B increases color temperature from 3400-5500 degrees Kelvin (commonly used with photoflood lamps)
80C increases color temperature from 3800-5500 degrees Kelvin (commonly used with flashbulbs)
80D increases color temperature from 4100-5500 degrees Kelvin (commonly used to remove extreme orange or red)
80A Color Conversion
2 (+1 stop)
Balances daylight film for use with most standard tungsten lighting, studio lighting and copy stand lighting
Used to shoot daylight film under artificial (household) lighting conditions
Increases color temperature from 3200-5500 degrees Kelvin