Leica E60 60mm UVa Filter for Noctilux M6 and M8 (13381)
Film, as well as video, often exhibits a greater sensitivity to what is to us invisible, ultraviolet light.  This is most often outdoors, especially at high altitudes, where the UV-absorbing atmosphere is thinner; and over long distances, such as marine scenes.  It can show up as a bluish color cast with color film, or it can cause a low-contrast haze that diminishes details, especially when viewing far-away objects, in either color or black-and-white.  Ultraviolet filters absorb UV light generally without affecting light in the visible region.