The bw 52mm kr 15 mrc skylight filter is a delicate reddish yellow conversion filter that absorbs violet and some blue plus a minimal amount of green but it passes yellow and red undiminished the colour of the light becomes warmer by 15 mired that is mostly the optimal amount for correcting the light blue cast in the shadows under a blue sky it also absorbs uv radiation and hence it provides better sharpness with colour films andor developing processes that generally yield results that