Sii filters: The narrow-band filter allows light from ionised sulphur atoms at 671.7 and 673.1 nanometres to pass through. These are the lines in which many planetary nebulae, emission nebulae and supernova remnants shine.
Astrophotography: Monochromatic cameras are best for this. Ideally, you should combine shots with sii, oii and h-alpha filters. This will give you an image that shows the delicate nebula structures clearly and with high contrast.
Line filters with a 12 nanometre half-width are useful if you are using a DSLR or a CCD camera with a higher dark current. The 12 nm filters are also the first choice if your camera has an integrated guiding chip, because when using 12 nm filters, you typically have twice as many stars in the image.
