A UVa filter is available as an accessory for every LEICA M lens.
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.