Safeguard your lens and absorb UV light. Film and video are more sensitive to UV light than our eyes are. This often shows up as a bluish cast in images, especially shots from high altitudes and long distances, particularly over water. UV filters are the most commonly used filters as they often provide better quality pictures. However that is not the reason why most photographers buy these filters. They use these filters to protect lenses as scratches on the lens surface are extremely annoying and sometimes visible in the photo. To reduce the chances of this screw a filter on the lens as it is cheaper to replace a filter rather than an expensive lens. A UV filter can always be left on the lens because there is almost no light loss.