2nd Quality CXB (formerly Astrodon) Narrowband Filters - 3nm NII Filter2nd Quality CXB (formerly Astrodon) 3 nm Narrowband NII Filter CXB (formerly Astrodon) 2nd Quality Filters are sold at a discount. 2nd Quality Filters are evaluated for edge chips, scratches, pinholes and inclusions. Although they have minor flaws, they still meet scientific standards. CXB (formerly Astrodon) 2nd Quality filters are still covered by our warranty for longevity, but are otherwise sold "as is" and are not returnable. 3nm NII Filter,