"The Baader Planetarium 8 nm SII CCD Filter delivers the absolute highest contrast deep sky images in H-Alpha, H-Beta, Oxygen III and Sulfur-II, with the shortest exposures possible. Their ultra-narrow bandwidths have extremely high transmissions, while completely rejecting light pollution as well as the important blocking of longer wavelengths.The high optical quality of the Baader Oxygen III filters guarantees no loss in sharpness or contrast. Each substrate is fine-optically polished plane parallel to deliver a smooth and accurate 1/4 wavefront over the entire surface. This special custom polishing operation sets Baader filters apart from the standard commercially precision-polished filter substrates used by most other filter manufacturers. Coatings are professionally applied by the most sophisticated equipment available, ensuring high consistency for bandpass centering and transmission. The ultra-hard ionbeam deposition ensures the coatings will never degrade from use or normal cleaning.In addition to their transmission properties, the Baader coatings were developed with another key goal in mind - eliminate the annoying reflections present in other narrowband astro-filters. To achieve this freedom from reflections, along with excellent out of band blocking, required careful design and testing of the coating stacks.Coatings are professionally applied in Germany by the most sophisticated equipment available today, ensuring high consistency for bandpas|True Optical Quality: Baader glass substrates are of true optical quality. Most other filters are merely made from raw flame-polished, ""optically flat,"" or sometimes a top quality commercially polished filter glass (fine for camera filters)|Filter Durability: Filter durability has always been a hallmark of Baader Planetarium. The multi-layer dielectric coatings are plasma-assisted and Ionbeam-hardened using the latest technology (the coatings are harder than the glass substrate itself.)|Stackability: Unlike other filters, this Baader Planetarium filter is truly designed to be stacked and combined. This is possible due to the high optical quality and highly efficient anti-reflection multicoatings|Special Filter Cell: Baader Planetarium's special filter cell design offers unique features that enhance their reliability and usability. Though difficult to produce, the ultra-thin filter cell results in the maximum possible clear aperture, in order"