The O-III line at 501nm is an important emission line of many Nebula objects and SN remnants. An extreme background contrast can be achieved even in urban areas with narrow-band filters.
The Altair Astro Premium Oiii 6.5nm filter is designed for astro imaging of nebulae with Mono CCD or CMOS cameras, blocking light pollution by cutting out the light pollution wavelengths. The filter blocks UV IR and has an anti-reflection AR coating.