Leica 13410 E39  Multi-Coated  Camera Lens  UV/IR Filter
The Leica filters for the Leica M system are made of optically pure glass, parallel plane ground and precisely annealed, so the full performance of the Leica M lenses is retained even with a filter attached. The UVa filter primarily performs the role of protecting the front element of the lens, and can be left permanently attached.