This OIII filter particularly enhances planetary nebulae in larger telescopes * Narrowband filter for high transmission, with high blocking of unwanted longer wavelengths to yield high-contrast images. * Ion beam technology and optical glass produces low scatter in a hard stable coating to reduce changes due to temperature and humidity. * Optical quality BK7 glass yields sharp star images even when filter is placed in front of diagonal. * 100% quality control: Every single filter is checked optically and cosmetically to assure performance. Every filter is individually serialized