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 O-III filter uses a characteristic property of the so called emmission nebulae. Those objekcts glow in special colors, the so called emmission lines. Those emmission lines are linked to chemical elements - in this case oxygen. The Explore Scientific O-III nebula filter blocks all other colors (and thereby nearly all of the artificial light) and only the two emmission lines of the oxygen can pass the filter. The result is astonoishing: suddenly nebulae are visible at locations that were completely empty without filters. In suburbian skies for example the veil nebula NGC 6992 is almost not visible with a 200mm telescope. By using this filter you can see the nebula and its structures without problems. A must for every visual observer. The Explore Scientific nebula filters come with a individual test certificate - your guarantee to receive a premium filter.