The OIII-CCD Filter is suitable for imaging of OIII nebulas from observation sites with light pollution and from dark sites as well. The contrast between an object glowing at 501nm and the background is increased enormous!
This SII-CCD Filter is suitable for imaging of SII-regions from observation sites with light pollution and from dark sites as well. The contrast between an object glowing at 672nm and the background is increased massively!
The Antlia H-Alpha (Ha) 3.0nm filter is suitable for imaging H-Alpha emissions from nebulae, planetary nebulae and supernova remnants. The 3.0nm bandwidth delivers a high transmission at a center wavelength of 656.3nm
Narrowband filter sets are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae
OIII 3nm Narrow Band filters isolate the doublet emission of doubly ionized Oxygen. After ionized hydrogen, this is the next most common emission when imaging nebulae.
SII filters isolate the emission from ionized Sulfur atoms, also common in nebulae. Emission is at two lines occurring as a doublet, at 671.6 and 673.1 nm.
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.
If you want the look of Hubble Space Telescope (HST) images, such as the famous “Pillars of Creation” (the Eagle Nebula, Messier 16), then the next filter to consider adding to your collection after H-a and OIII is the SII.
Narrowband filter sets are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae
Astrodon LRGB Gen2 E-Series Tru-Balance filters have revolutionized CCD imaging. Their popularity is due to their ease-of-use, high optical throughput and great resulting colors for galaxies, star clusters and nebulae.
This is a bit complicated. It is not well known that most H-a filters pass both H-a and NII. H-a emits at 656.3 nm and NII emits most strongly at 658.4 nm (and weakly at 653.8 nm). These are very close together spectrally.