Astrodon 3 nm Narrowband Filters – OIII 3nm
The next filter to complement your LRGBH-a set is an oxygen filter. OIII (“ohthree”) emits light near 500 nm and is a blue-green- or teal-colored filter. Many of my images of planetary nebula and supernova remnants are taken only with H-a and OIII filters. They show great structural detail, but have natural colors, looking like an RGB image.
Astrodon OIII filters have a center bandwidth of 500.1 nm.