Ultraviolet filters, such as the Hoya UV(0), also known as haze filters, are used to block the rays that make long-distance fine-weather views hazy or indistinct. UV rays focus slightly in front of a film or sensor and may, when an aperture is wide open, result in poor definition. Degradation caused by ultraviolet radiation generally increases with altitude above sea level, so it is in long-distance views of high mountains, aerial views, sunlit sow scenes that the effect may be most noticeable. Views taken near water may also be improved. They can be used for colour or black-and-white photography.