The B+W 55mm Slim MRC Clear UV Haze (010) Filter blocks the invisible UV component of light from the sky, which can cause blur & a blue cast. UV Filters are ideal for photography in high altitudes (in the mountains), by the sea & in regions with very clean air. Because the glass is colourless, colour rendition is not altered, aside from the elimination of the unwanted blue cast, & no increase in exposure is required. That makes a UV Filter very suitable as protection of the front element of the taking lens against dust, s&, sea water spray & the like, & it can be kept on the lens at all times.