The Heliopan 49mm KB-15 (80A) Color Conversion Filter is blue. It is 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.
Heliopan has been a leader in the filter industry since 1949. They are known for their high quality and production standards. Their slim mounts facilitate using them with wider angle lenses. Heliopan offers most of their filters with either their standard hard coating or with their industry leading SH-PMC 16 layer multi-coating that transmits over 99.5% of the light striking it on to the image plane for the lowest flare and greatest color saturation.