Filter blocks ultraviolet rays. Ultraviolet rays make your pictures blue, and photographs taken with monochrome films hazy. Most effective for distant objects. A "MUST" filter for shooting in coastal and mountains areas in fine weather.
Single coated, Leica thread pitch, also for use of Leica Elmar 50mm F3.5 or Elmar 3.5cm F3.5. Has no female thread in front.