The 49mm 81A (KR3) Filter from Heliopan controls the bluish coloration that affects daylight film. Even though the human eye automatically adjusts to various lighting conditions, film does not. Irrespective of the light source, a white sheet of paper will always "appear" white to the human eye. However, when photographed under various lighting sources, the paper will reproduce a representation of the light it was shot under. An 81A filter will allow you to correct for this white balancing problem when you wish to reduce the color temperature of the shot and bring your tones back to a more acceptable level.