One of the most important obstacles for the exploration of the night sky is the brightening of the night sky by artificial lights, such as streetlights. The night sky is not really dark in the vicinity of towns or cities, which reduces the visibility of objects bejond the solar systems enourmously. Depending on the type of the celestial object it is possible to increase the contrast dramatically by blocking the annoying artifical light. The Explore Scientific UHC filter uses a characteristic property of the artificial illumination. Streetlights and lamps shine in special colors - the typical colors of high-pressure or mercury lamps. The Explore Scientific CLS nebula filter blocks those colors and thereby increases contrast - the light ot the celestial objects can pass the filter. The result is astonishing: suddenly objects are visible at locations that were completely empty without filters. In suburbian skies for example the large galaxy M101, the Veil-nebula Ngc 6992 or even the bright Dumbell-nebula M27are not clearly visible. By using this filter you can see the nebulae and their structures. A must for every visual observer. The Explore Scientific nebula filters come with a individual test certificate - your guarantee to receive a premium filter.