SII filters: The narrow-band filter allows light from ionised sulphur atoms at 650 nanometres to pass through. This is the line in which many planetary nebulae, emission nebulae and supernova remnants shine.
Astrophotography: Monochromatic cameras are best used. Ideally, combine shots with SII, OIII and H-alpha filters. This results in an image that shows the delicate nebula structures in high contrast and clearly.
The narrow passband of this filter, with a bandwidth of only 6.5 nanometres, works even under difficult city conditions to bring out faint planetary nebulae, emission nebulae and supernova remnants, or make them visible in the first place.
