SIRIUS 1.25IN UHC SKYGLOW BROADBAND CLS FILTER is for visual deep-sky observation. It lets almost 100-percent of the radiation from both O-III lines and the H-beta line pass through. A second bandpass for the H-alpha line ensures that this radiation also reaches the eye, and scattered light from other wavelength ranges is also filtered out. Due to the strong reduction of the sky background, gas and planetary nebulas are visible with an unexpected abundance of detail. Because of the high transmission, the UHC filter provides enough light to successfully observe deep-sky objects with smaller telescopes.