The phot rreg slim uv ultra violet filter the phot rreg slim uv ultra violet filter is a general use clear filter that helps to absorb ultraviolet light and reduce the bluish cast of daylight this filter is especially useful when photographing at high altitudes or around bodies of water no additional coloration or contrast is provided the uv filter is also useful as a general protective filter to leave on lenses at all times filters help to reduce dirt and moisture from reaching your