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)
DayStar
Filters 0.5Å H-alpha Quantum PE filter
$ 27,500.00
ready for shipping in 3-6
months
Optolong
Filters L-Ultimate 2"
$ 420.00
ready for shipping in 24
h
Lunt Solar Systems
Filters LS 100F Ha H-Alpha filter set for 3400mm focal length
$ 14,800.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters LS 100F Ha H-Alpha filter set for 1800mm focal length
$ 13,200.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters 100mm Ha Etalon filter with B1800 for 2" focuser
$ 13,200.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters LS 100F Ha H-Alpha filter set for 1200mm focal length
$ 12,600.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters 100mm Ha Etalon filter with B1200 for 2" focuser
$ 12,600.00
ready for shipping in 1-2
weeks
Coronado
Filters Double Stacking Etalon Solarmax II PST 40mm
$ 1,570.00
ready for shipping in 24
h
Lunt Solar Systems
Filters LS 100F Ha H-Alpha filter set for 600mm focal length
$ 11,900.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters 100mm Ha Etalon filter with B600 for 2" focuser
$ 11,900.00
ready for shipping in 1-2
weeks
Optolong
Filters SHO Filter Kit 3nm 2"
$ 1,360.00
ready for shipping in 3-5
weeks
DayStar
QUARK Magnesium I (b2) Line
$ 2,200.00
Sale price:
$ 1,979.94
ready for shipping in 24
h
Lunt Solar Systems
Solar Filters Ca-K module for LS130MT/B3400
$ 3,690.00
ready for shipping in 1-2
weeks
Optolong
Filters SHO Filter Kit 2"
$ 760.00
ready for shipping in 24
h
Coronado
Filters SolarMax III H-Alpha-Etalon 90mm BF30
$ 7,000.00
Product can be shipped as of 01.04.2025
Lunt Solar Systems
Filters H-alpha double-stack solar filter LS100FHa
RRP:
$ 11,600.00
Our price:
$ 11,200.00
ready for shipping in 1-2
weeks
Omegon
Filters Pro 2'' SII CCD filter
( 1 / 5 )
$ 189.00
ready for shipping in 24
h
Lunt Solar Systems
Filters LS50C double-stack filter
$ 1,790.00
ready for shipping in 1-2
weeks
Baader
Filters H-alpha/OIII/SII CMOS f/2 Ultra-Highspeed 2"
$ 1,160.00
ready for shipping in 1-2
weeks
Baader
Filters H-alpha/OIII/SII CMOS Ultra-Narrowband 2"
$ 1,100.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters LS60FHa B3400 2" etalon filter system
$ 6,900.00
ready for shipping in 1-2
weeks
Omegon
Filters Pro 1.25'' OIII CCD filter
$ 129.00
ready for shipping in 24
h
Explore Scientific
Filters SII 6.5nm 2"
RRP:
$ 242.00
Our price:
$ 122.00
ready for shipping in 24
h
Explore Scientific
Filters H-alpha 7nm 2"
$ 242.00
ready for shipping in 24
h
IDAS
Filters SHO Filter Set 50.8mm
$ 1,340.00
ready for shipping in 3-5
weeks
Optolong
Filters SII Filter 2"
RRP:
$ 252.00
Our price:
$ 242.00
ready for shipping in 24
h
DayStar
QUARK H-alpha filter Gemini
$ 3,680.00
ready for shipping in 3-6
months
Lunt Solar Systems
Filters 50mm Ha Etalon filter
$ 2,060.00
ready for shipping in 1-2
weeks
Explore Scientific
Filters H-alpha 12nm 1.25"
$ 168.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters LS 50F Ha H-Alpha filter set for 3400mm focal length
$ 5,600.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters LS60FHa B1800 2" etalon filter system
$ 5,300.00
ready for shipping in 1-2
weeks
Lunt Solar Systems
Filters LS60FHa B1800 1.25" etalon filter system
$ 5,300.00
ready for shipping in 1-2
weeks
Explore Scientific
Filters OIII 6.5nm 1.25"
RRP:
$ 168.00
Our price:
$ 85.00
ready for shipping in 24
h
DayStar
Combo QUARK H-Alpha solar filter, for chromosphere
RRP:
$ 1,890.00
Our price:
$ 1,700.00
ready for shipping in 24
h
Astronomik
Filters 2" OIII filter
$ 210.00
ready for shipping in 24
h
Omegon
Filters Pro 1.25'' SII CCD filter
$ 129.00
ready for shipping in 24
h