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)](/CMS/images/text/glossary/Emissionslinien_Wikipedia.png)
![Omegon Filters Pro 1.25'' OIII CCD filter](/Produktbilder/normal/47292_1/Omegon-Filters-Pro-1-25-OIII-CCD-filter.jpg)
Omegon
Filters Pro 1.25'' OIII CCD filter
$ 139.00
![Omegon Filters Pro 2'' OIII CCD filter](/Produktbilder/normal/47293_1/Omegon-Filters-Pro-2-OIII-CCD-filter.jpg)
Omegon
Filters Pro 2'' OIII CCD filter
$ 179.00
![Omegon Filters Pro 2'' SII CCD filter](/Produktbilder/normal/47295_1/Omegon-Filters-Pro-2-SII-CCD-filter.jpg)
Omegon
Filters Pro 2'' SII CCD filter
$ 189.00
![Omegon Filters OIII filter 1.25''](/Produktbilder/normal/15625_1/Omegon-Filters-OIII-filter-1-25-.jpg)
Omegon
Filters OIII filter 1.25''
$ 89.00
![Baader Filters OIII CMOS Narrowband 65x65mm](/Produktbilder/normal/70864_1/Baader-Filters-OIII-CMOS-Narrowband-65x65mm.jpg)
Baader
Filters OIII CMOS Narrowband 65x65mm
$ 382.00
![Baader Filters OIII CMOS f/2 Highspeed 36mm](/Produktbilder/normal/70916_1/Baader-Filters-OIII-CMOS-f-2-Highspeed-36mm.jpg)
Baader
Filters OIII CMOS f/2 Highspeed 36mm
$ 186.00
![Baader Filters OIII CMOS f/2 Ultra-Highspeed 36mm](/Produktbilder/normal/70937_1/Baader-Filters-OIII-CMOS-f-2-Ultra-Highspeed-36mm.jpg)
Baader
Filters OIII CMOS f/2 Ultra-Highspeed 36mm
$ 341.00
![Baader Filters OIII CMOS f/2 Ultra-Highspeed 50.4mm](/Produktbilder/normal/70939_1/Baader-Filters-OIII-CMOS-f-2-Ultra-Highspeed-50-4mm.jpg)
Baader
Filters OIII CMOS f/2 Ultra-Highspeed 50.4mm
$ 416.00
![Baader Filters OIII CMOS f/2 Ultra-Highspeed 50x50mm](/Produktbilder/normal/70940_1/Baader-Filters-OIII-CMOS-f-2-Ultra-Highspeed-50x50mm.jpg)
Baader
Filters OIII CMOS f/2 Ultra-Highspeed 50x50mm
$ 429.00
![Baader Filters H-alpha CMOS Narrowband 65x65mm](/Produktbilder/normal/70857_1/Baader-Filters-H-alpha-CMOS-Narrowband-65x65mm.jpg)
Baader
Filters H-alpha CMOS Narrowband 65x65mm
$ 387.00
![Baader Filters H-alpha CMOS Ultra-Narrowband 50.4mm](/Produktbilder/normal/70876_1/Baader-Filters-H-alpha-CMOS-Ultra-Narrowband-50-4mm.jpg)
Baader
Filters H-alpha CMOS Ultra-Narrowband 50.4mm
$ 446.00
![Baader Filters H-alpha CMOS f/2 Highspeed 31mm](/Produktbilder/normal/70908_1/Baader-Filters-H-alpha-CMOS-f-2-Highspeed-31mm.jpg)
Baader
Filters H-alpha CMOS f/2 Highspeed 31mm
$ 167.00
![Baader Filters H-alpha CMOS f/2 Highspeed 36mm](/Produktbilder/normal/70909_1/Baader-Filters-H-alpha-CMOS-f-2-Highspeed-36mm.jpg)
Baader
Filters H-alpha CMOS f/2 Highspeed 36mm
$ 189.00
![Baader Filters H-alpha CMOS f/2 Highspeed 50x50mm](/Produktbilder/normal/70912_1/Baader-Filters-H-alpha-CMOS-f-2-Highspeed-50x50mm.jpg)
Baader
Filters H-alpha CMOS f/2 Highspeed 50x50mm
$ 317.00
![Baader Filters H-alpha CMOS f/2 Highspeed 65x65mm](/Produktbilder/normal/70913_1/Baader-Filters-H-alpha-CMOS-f-2-Highspeed-65x65mm.jpg)
Baader
Filters H-alpha CMOS f/2 Highspeed 65x65mm
$ 393.00
![Baader Filters H-alpha CMOS f/2 Ultra-Highspeed 31mm](/Produktbilder/normal/70929_1/Baader-Filters-H-alpha-CMOS-f-2-Ultra-Highspeed-31mm.jpg)
Baader
Filters H-alpha CMOS f/2 Ultra-Highspeed 31mm
$ 307.00
![Baader Filters H-alpha CMOS f/2 Ultra-Highspeed 36mm](/Produktbilder/normal/70930_1/Baader-Filters-H-alpha-CMOS-f-2-Ultra-Highspeed-36mm.jpg)
Baader
Filters H-alpha CMOS f/2 Ultra-Highspeed 36mm
$ 371.00
![Baader Filters SII CMOS Ultra-Narrowband 31mm](/Produktbilder/normal/70887_1/Baader-Filters-SII-CMOS-Ultra-Narrowband-31mm.jpg)
Baader
Filters SII CMOS Ultra-Narrowband 31mm
$ 286.00
![Baader Filters f/2 Highspeed SII CMOS 1.25"](/Produktbilder/normal/70921_1/Baader-Filters-f-2-Highspeed-SII-CMOS-1-25-.jpg)
Baader
Filters f/2 Highspeed SII CMOS 1.25"
$ 158.00
![Baader Filters SII CMOS f/2 Ultra-Highspeed 36mm](/Produktbilder/normal/70944_1/Baader-Filters-SII-CMOS-f-2-Ultra-Highspeed-36mm.jpg)
Baader
Filters SII CMOS f/2 Ultra-Highspeed 36mm
$ 348.00
![Baader Filters SII CMOS f/2 Ultra-Highspeed 2"](/Produktbilder/normal/70945_1/Baader-Filters-SII-CMOS-f-2-Ultra-Highspeed-2-.jpg)
Baader
Filters SII CMOS f/2 Ultra-Highspeed 2"
$ 397.00
![Baader Filters SII CMOS f/2 Ultra-Highspeed 50x50mm](/Produktbilder/normal/70947_1/Baader-Filters-SII-CMOS-f-2-Ultra-Highspeed-50x50mm.jpg)
Baader
Filters SII CMOS f/2 Ultra-Highspeed 50x50mm
$ 429.00
![Baader Filters H-alpha/OIII/SII CMOS f/2 Highspeed 31mm](/Produktbilder/normal/70950_1/Baader-Filters-H-alpha-OIII-SII-CMOS-f-2-Highspeed-31mm.jpg)
Baader
Filters H-alpha/OIII/SII CMOS f/2 Highspeed 31mm
$ 479.00
![Omegon Filters 7nm H-alpha 1.25 pro filter](/Produktbilder/normal/60111_1/Omegon-Filters-7nm-H-alpha-1-25-pro-filter.jpg)
Omegon
Filters 7nm H-alpha 1.25 pro filter
$ 199.00
![Omegon Filters Pro 1.25'' SII CCD filter](/Produktbilder/normal/47294_1/Omegon-Filters-Pro-1-25-SII-CCD-filter.jpg)
Omegon
Filters Pro 1.25'' SII CCD filter
$ 139.00
![Omegon Filters UHC Filter, 2"](/Produktbilder/normal/15628_1/Omegon-Filters-UHC-Filter-2-.jpg)
Omegon
Filters UHC Filter, 2"
$ 99.00
![Omegon Filters OIII Filter 2"](/Produktbilder/normal/15627_1/Omegon-Filters-OIII-Filter-2-.jpg)
Omegon
Filters OIII Filter 2"
$ 119.00
![Omegon Filters Pro 1.25'' H-alpha filter](/Produktbilder/normal/47298_1/Omegon-Filters-Pro-1-25-H-alpha-filter.jpg)
Omegon
Filters Pro 1.25'' H-alpha filter
$ 149.00
![Omegon Filters Pro 2'' H-alpha filter](/Produktbilder/normal/47299_1/Omegon-Filters-Pro-2-H-alpha-filter.jpg)
Omegon
Filters Pro 2'' H-alpha filter
$ 209.00
![Omegon Filters Pro 1.25'' H-Beta filter](/Produktbilder/normal/47300_1/Omegon-Filters-Pro-1-25-H-Beta-filter.jpg)
Omegon
Filters Pro 1.25'' H-Beta filter
$ 99.00
![Omegon Filters Pro 2'' H-Beta filter](/Produktbilder/normal/47301_1/Omegon-Filters-Pro-2-H-Beta-filter.jpg)
Omegon
Filters Pro 2'' H-Beta filter
$ 139.00
![Coronado Filters SolarMax III H-Alpha-Etalon 60mm BF10](/Produktbilder/normal/59478_2/Coronado-Filters-SolarMax-III-H-Alpha-Etalon-60mm-BF10.jpg)
Coronado
Filters SolarMax III H-Alpha-Etalon 60mm BF10
$ 2,470.00
![Coronado Filters SolarMax III H-Alpha-Etalon 90mm BF30](/Produktbilder/normal/59473_1/Coronado-Filters-SolarMax-III-H-Alpha-Etalon-90mm-BF30.jpg)
Coronado
Filters SolarMax III H-Alpha-Etalon 90mm BF30
$ 7,100.00
![Coronado Filters SolarMax III H-Alpha-Etalon 60mm BF15](/Produktbilder/normal/59478_2/Coronado-Filters-SolarMax-III-H-Alpha-Etalon-60mm-BF15.jpg)
Coronado
Filters SolarMax III H-Alpha-Etalon 60mm BF15
$ 2,680.00
![Coronado Filters SolarMax III H-Alpha-Etalon 60mm BF30](/Produktbilder/normal/59478_1/Coronado-Filters-SolarMax-III-H-Alpha-Etalon-60mm-BF30.jpg)
Coronado
Filters SolarMax III H-Alpha-Etalon 60mm BF30
$ 4,080.00
![Lumicon Filters H-Beta filter 1.25''](/Produktbilder/normal/6747_4/Lumicon-Filters-H-Beta-filter-1-25-.jpg)