As their names suggests, these filters use HOYA colored glass. They are used for color correction of different light sources when using colour film, or for controlling contrast with Black & White film. Color correction filters are important as colour films do not have the flexibility of the human eye to automatically adjust to different situations. Black & White films register colours as shades of grey and the rendition of each colour in a scene is important, so filters can be used to control this. The colour of the glass used in all these filters is carefully controlled and to reduce the possibility of colour shift over a period of time, as such high quality filters are coated or multicoated on both sides. This maintains the desired effect and gives a long service life.
These are color conversion filters for the use of daylight type color films with artificial light source. 80B increases the color temperature from 3400°K to 5500°K for the use of photoflood lamps.