Line filters selectively allow only light from a specific spectral line to pass through. OIII, SII and H-alpha filters are especially popular.
The Roman numerals III and II indicate the degree of ionisation of the chemical element that produces the spectral line. So OIII (pronounce oh three) stands for doubly ionised oxygen, and SII for singly ionised sulphur. OI and SI indicate the electrically neutral atoms.
Line filters are ideal for the visual observation and photography of emission nebulae, supernova remnants and planetary nebulae, since these objects produce defined spectral lines. Star clusters and galaxies on the other hand have a continuous spectrum. For these, filters that generally suppress the sky’s brightness (CLS or UHC filters) are more suitable.
Example of an emission line spectrum (source: Wikipedia)
Baader
Filters SII CMOS Ultra-Narrowband 2"
$ 443.00
Omegon
Filters Pro 2'' SII CCD filter
$ 179.00
Chroma
Filters SII 8nm 2"
RRP:
$ 1,360.00
Our price:
$ 1,270.00
Chroma
Filters Filter SII 36mm unmounted, 3nm
RRP:
$ 1,360.00
Our price:
$ 1,190.00
Astronomik
Filters SII 12nm Clip Sony alpha 7
$ 387.00
Baader
Filters SII CMOS f/2 Ultra-Highspeed 65x65mm
$ 660.00
Baader
Filters SII CMOS f/3 Ultra-Highspeed 65x65mm
$ 650.00
Baader
Filters SII CMOS Ultra-Narrowband 65x65mm
$ 650.00
Askar
Filters Colour Magic SII 3nm 2"
RRP:
$ 550.00
Our price:
$ 530.00
Astronomik
Filters SII 6nm CCD MaxFR Clip Nikon XL
$ 800.00
Astronomik
Filters SII 6nm CCD MaxFR Clip Canon EOS R XL
$ 800.00
Astronomik
Filters SII 6nm CCD MaxFR Clip Sony alpha 7
$ 800.00
