The S-II 6.5nm 2" filter from Explore Scientific is designed to facilitate the observation of deep-sky objects, such as planetary nebulae, emission nebulae, and supernova remnants, even in challenging urban observation conditions. This narrowband filter blocks almost all artificial light and only allows the emission line of ionized sulfur at 672 nm to pass through, thereby revealing details invisible to the naked eye without a filter. With a bandwidth of only 6.5 nm, it significantly increases the contrast and sharpness of faint celestial objects. This filter is ideal for amateur astronomers as well as for astrophotography.