Increases contrast between reds and yellows. Particularly useful for distant outdoor shots taken with a telephoto lens. Also useful in color photography for spectacular sunsets, seascapes, etc.
To provide photographers with a higher quality professionals require, Hoya created the Multi-coated line of filters. These filters have a 3 layer coating system that further reduces light reflections off the surfaces of the glass, the average is only 1-2%.
This means that 98-99% of the light striking the filter is going through it, and depending on the type of filter, into the camera lens and onto the film. These layers of anti-reflective coating are bonded to the surface of the glass in a furnace at a temperature of up to 800 degrees F.