This (C) lens filter absorbs the ultraviolet rays, which often makes outdoor photographs hazy and indistinct. Also serves to protect the lens from scratching, dirt, and dust. Plus, this UV filter does not cut down (97% effective transmission) on light coming into the lens unlike non coated filters. All new slim frame is compatible with wide-angle lenses and is double-threaded, which allows use of regular snap-on lens caps or allows other filters to be stacked on top.