The Heliopan 37mm KB-18 Filter is a color conversion filter that helps to increase the color temperature from about 2600 to 5500K. This blue filter allows you to use daylight-balanced film in 40W tungsten lighting without any color casts due to the lighting.
There is a 4.5x filter factor with this filter, requiring an increase of 2.6 stops for normal exposure. It has a 37mm brass mounting ring that is painted a matte black to help reduce reflections. The SH-PMC multi-coated Schott glass provides greater contrast and reduced reflection compared to uncoated filters.