The Tiffen 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.
Tiffen makes the 80 series of filters in many sizes to accommodate the many uses this filter has. This filter can be used by the pro and amateur alike, weekend photo warrior or pro cinematographer and must be considered an essential addition to any photo arsenal.