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)
Optolong
Filters L-Ultimate 2"
$ 418.00
ready for shipping in 24
h
Omegon
Filters OIII Filter 2"
( 5 / 5 )
$ 119.00
ready for shipping in 24
h
Omegon
Filters OIII filter 1.25''
$ 89.00
ready for shipping in 24
h
Optolong
Filters L-Ultimate 1,25"
$ 272.00
ready for shipping in 24
h
Omegon
Filters Pro 2'' SII CCD filter
( 1 / 5 )
$ 189.00
ready for shipping in 24
h
Omegon
Filters Pro 2'' OIII CCD filter
$ 179.00
ready for shipping in 24
h
Optolong
Filters SHO Filter Kit 1,25"
$ 550.00
ready for shipping in 24
h
Optolong
Filters SHO Filter Kit 2"
$ 750.00
ready for shipping in 24
h
Optolong
Filters SII Filter 2"
RRP:
$ 251.00
Our price:
$ 240.00
ready for shipping in 24
h
DayStar
Combo QUARK H-Alpha solar filter, for chromosphere
RRP:
$ 1,880.00
Our price:
$ 1,690.00
ready for shipping in 24
h
Omegon
Filters Pro 1.25'' H-Beta filter
$ 99.00
ready for shipping in 24
h
Optolong
Filters SHO Filter Kit 3nm 2"
$ 1,350.00
ready for shipping in 3-5
weeks
Coronado
Filters Double Stacking Etalon Solarmax II PST 40mm
$ 1,560.00
ready for shipping in 24
h
Omegon
Filters Pro 2'' H-alpha filter
$ 209.00
Product can be shipped as of 15.03.2025
DayStar
Filters 0.5Å H-alpha Quantum PE filter
$ 27,400.00
ready for shipping in 3-6
months
Baader
Solar Filter SunDancer II TZ-3S H-alpha 2"/1.25"
$ 3,710.00
ready for shipping in 3-7
days
STC
Filters Duo-NB Clip Canon (Full Frame)
$ 491.00
ready for shipping in 1-2
weeks
Omegon
Filters 7nm H-alpha 1.25 pro filter
$ 199.00
ready for shipping in 24
h
Baader
Filters H-alpha/OIII/SII CMOS f/2 Ultra-Highspeed 2"
$ 1,160.00
ready for shipping in 1-2
weeks
Astronomik
Filters 1.25" OIII filter
$ 104.00
ready for shipping in 24
h
Omegon
Filters Pro 1.25'' OIII CCD filter
$ 129.00
ready for shipping in 24
h
Omegon
Filters Pro 1.25'' H-alpha filter
$ 149.00
ready for shipping in 24
h
Baader
Filters H-alpha/OIII/SII CMOS f/2 Highspeed 1.25"
$ 439.00
ready for shipping in 1-2
weeks
Omegon
Filters Pro 1.25'' SII CCD filter
$ 129.00
ready for shipping in 24
h
Astronomik
Filters H-alpha 12nm CCD Clip-Filter Sony alpha
$ 355.00
ready for shipping in 3-7
days
Baader
Filters K-LINE filter gestackt, 1 ¼ " (with 3,8 astro+solarly 200x290mm photo film)
$ 299.00
ready for shipping in 1-2
weeks
Sharpstar
Filters D Duo-Band Filter SII & OIII 2"
$ 282.00
ready for shipping in 24
h
Omegon
Filters Pro 2'' H-Beta filter
$ 139.00
ready for shipping in 24
h
Baader
Filters H-alpha/OIII/SII CMOS Ultra-Narrowband 2"
$ 1,100.00
Product can be shipped as of 12.03.2025
Astronomik
Filters OIII 6nm CCD MaxFR 2"
$ 720.00
ready for shipping in 3-7
days
Astronomik
Filters SII 6nm CCD MaxFR 2"
$ 720.00
ready for shipping in 3-7
days
IDAS
Filters OIII 6.0nm 2
$ 418.00
ready for shipping in 3-5
weeks
Baader
Filters H-alpha 20nm 2"
$ 173.00
ready for shipping in 24
h
Baader
Filters OIII CMOS Narrowband 50.4mm
$ 288.00
ready for shipping in 1-2
weeks
Astronomik
Filters H-beta 2"
$ 209.00
ready for shipping in 3-7
days
Baader
Filters H-alpha/OIII/SII CMOS Narrowband 36mm
$ 487.00
ready for shipping in 1-2
weeks