The Hoya 52mm 81B Hoya Multi-Coated (HMC) Glass filter controls the bluish coloration that affects daylight film. It can also remove excessive blue from the effects of electronic flash. It's Autumn. The clouds are low hanging and the sky is patchy blue. You've gone for a ride upstate to the mountains and the light in open shade is bluish. A photo taken of your girlfriend with daylight balanced film leaning against the side of a barn will yield bluish tones that she might not find particularly flattering. An 81B filter will replace even more yellow than an 81A and bring her skin tones back to a more appealing level. An 81B can also be used with electronic flash to reduce the amount of blue generated by the flash. The 81 series (81A, B, C, D and EF) allows you to choose how much warmth you wish to replace in the image.