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"
$ 415.00
ready for shipping in 24
h
Omegon
Filters OIII filter 1.25''
$ 79.00
ready for shipping in 24
h
Omegon
Filters OIII Filter 2"
( 5 / 5 )
$ 99.00
ready for shipping in 24
h
DayStar
QUARK H-alpha filter,chromosphere
$ 1,840.00
ready for shipping in 24
h
Optolong
Filters SHO Filter Kit 7nm 2"
$ 970.00
ready for shipping in 3-5
weeks
Optolong
Filters SII 6.5nm 2"
$ 254.00
ready for shipping in 24
h
Astronomik
Filters 1.25" OIII filter
$ 115.00
ready for shipping in 24
h
DayStar
QUARK Calcium-H-Line
$ 1,840.00
ready for shipping in 24
h
Optolong
Filters L-Ultimate 1,25"
$ 311.00
ready for shipping in 24
h
Lunt Solar Systems
Filters H-alpha double-stack for LS60FHa
RRP:
$ 3,930.00
Our price:
$ 2,620.00
ready for shipping in 1-2
weeks
Omegon
Filters Pro 1.25'' H-Beta filter
$ 99.00
ready for shipping in 24
h
DayStar
QUARK H-alpha filter, prominences
$ 1,840.00
ready for shipping in 24
h
DayStar
Filters 0.5Å H-alpha Quantum PE filter
$ 27,200.00
ready for shipping in 3-6
months
Omegon
Filters 7nm H-alpha 1.25 pro filter
$ 199.00
ready for shipping in 24
h
Optolong
Filters SHO 3nm 2"
$ 1,160.00
ready for shipping in 3-5
weeks
Omegon
Filters Pro 2'' SII CCD filter
( 1 / 5 )
$ 179.00
ready for shipping in 24
h
Astronomik
Filters H-alpha 12nm CCD Clip Canon EOS APS-C
$ 230.00
ready for shipping in 24
h
Astronomik
Filters HSO 6nm 36mm
$ 870.00
ready for shipping in 3-7
days
ZWO
Filters Narrowband Filter Set H-alpha, SII, OIII 2"
$ 1,160.00
ready for shipping in 24
h
Omegon
Filters Pro 2'' H-Beta filter
$ 129.00
ready for shipping in 24
h
Omegon
Filters Pro OIII 7nm Filter 1,25"
$ 199.00
ready for shipping in 24
h
Omegon
Filters Pro SII 7nm Filter 1.25"
$ 199.00
ready for shipping in 24
h
Lunt Solar Systems
Filters LS50C double-stack filter
RRP:
$ 1,970.00
Our price:
$ 1,380.00
ready for shipping in 24
h
Baader
Filters K-LINE filter gestackt, 1 ¼ " (with 3,8 astro+solarly 200x290mm photo film)
$ 330.00
ready for shipping in 1-2
weeks
Astronomik
Filters H-alpha 12nm CCD Clip-Filter Sony alpha
$ 392.00
ready for shipping in 3-7
days
ZWO
Filters Filter set H-alpha, SII, OIII 36mm unmounted
$ 810.00
ready for shipping in 3-5
weeks
Astronomik
Filters 2" OIII filter
$ 230.00
ready for shipping in 24
h
Baader
Filters H-alpha/OIII/SII CMOS Ultra-Narrowband 1.25"
$ 840.00
ready for shipping in 1-2
weeks
Optolong
Filters SHO Filter Kit 1,25"
RRP:
$ 640.00
Our price:
$ 510.00
ready for shipping in 24
h
Optolong
Filters H-alpha 3nm 2"
$ 450.00
ready for shipping in 24
h
Coronado
Filters Double Stacking Etalon Solarmax II PST 40mm
$ 1,380.00
Sale price:
$ 1,165.80
ready for shipping in 24
h
Baader
Filters H-alpha CMOS Narrowband 1.25"
$ 161.00
ready for shipping in 1-2
weeks
Baader
Filters OIII CMOS Narrowband 1.25"
$ 158.00
ready for shipping in 1-2
weeks
Baader
Filters Ultra-Narrowband SII CMOS 50.4mm
$ 450.00
ready for shipping in 1-2
weeks
Astronomik
Filters H-alpha 12nm MaxFR XT Clip EOS R XL
$ 570.00
ready for shipping in 1-2
weeks
Astronomik
Filters H-alpha 12nm MaxFR XT Clip Nikon XL
$ 570.00
ready for shipping in 1-2
weeks