Product description this high quality sigma uv filter blocks the invisible uv component of light from the sky which can cause blur and often a blue cast uv filters are ideal for photography in high altitudes by the sea and in regions with very clean air the pictures gain brilliance and disturbing blue casts are avoided as the glass is colourless colour rendition is not altered aside from the elimination of the unwanted blue cast and no increase in exposure is required the colourless glass also m