Astronomik H-alpha 6nm Narrowband CCD Filter

Astronomik H-alpha 6nm Narrowband CCD Filter

  (4 Reviews)
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About this product

Model:  ak_ha-ccd_6nm_125
Part Number:  10212550

The Astronomik H-alpha Filter is suitable for imaging of Hydrogen nebulas from observation sites with light pollution and from dark sites as well. The contrast between an object glowing at 656nm and the background is increased enormously!

Due to the combination of the narrow bandwidth of 6nm and the high transmission of typically 96% the filter gives you an contrast boost, as all unwanted light from other wavelengths than 656nm is blocked form UV up to the IR. This results in an very dark background compared with any filters with a higher bandwidth

The FWHM of 6nm is matched to give you optimal performance with CCD and CMOS sensors with a very low dark current! The 6nm filter is the best choice if you are observing from a heavily light polluted site or if you are imaging faint objects in star-crowded regions of the milky-way.

Due to the new MFR coating technique you may use one single filter on all instruments up to f/3 without a significant reduction in performance.

The Astronomik H-alpha filter MUST NOT BE USED for solar observation!


  • Guaranteed Transmission of more than 90% at the H-alpha Line (656 nm)
  • Typical Transmission of 96% at the H-alpha Line (656 nm)
  • Full-Width-Half Maximum (FWHM): 6nm
  • Perfect blocking of unwanted light from UV up to the IR
  • MFR Coating technique: Usable with all optics up to f/3
  • Optically polished substrate, striae-free and free of residual stresses
  • Not sensitive to high humidity or ageing effects
  • Scratch-resistance!
  • Excellent quality substrate, diffraction limited - the optical performance of your telescope will not be reduced
  • Parfocal with other Astronomik filters
  • 1mm Glass Thickness
  • Supplied in a high-quality, long lasting, filter box

Imaging with Narrowband Filters

If you have to observe from light polluted sites (like most of us...), imaging with narrowband filters is the best way to take great images, as all kind of light pollution can be blocked very effective! Normally an H-alpha filter should be your first step into this amazing field of astrophotography! With an Narrowband H-alpha filter you will be able to take deep and contrasty images even with very heavy light pollution or with the full moon high up in the sky!

If you look at other astro-photos, an H-alpha is the best choice for all nebulas glowing red! An OIII filters expands your imaging possibilities, as you are able to image all greenish/blueish structures. Planetary nebulas and star forming regions are great targets! The SII filters completes your HSO-set of filters. With these three filters you are able to process your images like the ones from the Hubble space telescope!

Operation of the filter

The filter blocks all unwanted light from artificial light-pollution, natural airglow and moonlight. Especially light from High- and Low-Pressure Sodium and mercury lights and all lines of natural airglow are 100% blocked. The filter increases the contrast between the sky-background and objects glowing at the H-alpha line at 656nm.

Tips and Hints for more applications

Using the H-alpha-CCD filter together with OIII-CCD and SII-CCD filters you make produce false-colour emission line images (HSO) in the same way as the Hubble-Space telescope. This is possible even from heavily light polluted sites!

The lower priced 12nm filters are the right choice for you, if you own a typical DSLR or a CCD camera with a high dark current! The 12nm filters should be the fist choice for cameras with an integrated guiding sensor, as you will have about twice as much stars compared to the 6nm filter.

Transmission Chart

  • The horizontal axis is the Wavelength in Nanometers (nm). 400nm is deep blue, at 520nm the human eye senses green and at 600nm red. At 656nm is the famous "H-Alpha" emission line of hydrogen.
  • The transmission in % is plotted on the vertical axis.
  • The blue line shows the transmission of the filter.
  • The most important emission lines from nebulas are shown in orange. The most important lines are from ionised Hydrogen (H-alpha and H-beta) and double ionised oxygen (OIII).

The major emission lines of artificial light pollution:
| Hg 435,8nm | Hg 546,1nm | Hg 577,0nm | Hg 578,1nm |
| Na 589,0nm | Na 589,6nm | Na 615,4nm | Na 616,1nm |

The major emission lines of nebulas:
H-β 486,1nm | OIII 495,9nm | OIII 500,7nm | H-α 656,3nm

Technical Data

  • Guaranteed Transmission of more than 90% at the H-alpha Line (656 nm)
  • Typical Transmission of 96% at the H-alpha Line (656 nm)
  • Full-Width-Half Maximum (FWHM): 6nm
  • Perfect blocking of unwanted light from UV up to the IR
  • Parfocal with all Astronomik filters
  • MFR Coating technique: Usable with all optics up to f/3
  • Thickness of 1mm
  • Not sensitive to moisture, scratch resistant or ageing
  • Optically polished substrate, striae-free and free of residual stresses
  • Astronomik filters are delivered in a high-quality, long lasting, filter box


Customer reviews

Average Rating (4 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
1,25 inch Ha filter
18 April 2021  | 

Excellent service as per standard from FLO and the filter came quickly to Sweden via DHL express. Fits perfectly into the EFW8 which I also purchased from FLO.
First tests have been very encouraging and I'm looking forward to acquiring the remaining SHO filters.

Rating (max 5):  
No Halos & Actually Parfocal!
20 January 2021  | 

I've come from Astronomik's clip in filters for Canon DSLRs, both full frame and APS-C. Those were great, albeit 12nm. Since going to an astro cam, I needed new filters. These are a really nice mid ground between the more expensive Chroma filters and since they changed their pricing, and the cheaper options which can vary in QC and transmission. Astronomik are the only real practical option for 2" narrowband filters at the moment.

I also own the UV IR L2 filter and interestingly, this 6nm Ha does seem to be par focal with it making life so much easier!

There appears to be no halos at all - I tested it on the horsehead with the infamous Alnitak, which often gives people problems (primarily with Oiii however) and I got pinpoint stars and no halos. I'd recommend everyone to go 6nm except DSLR and RASA users. The difference between 12nm and 6nm is quite stark and will result in much more manageable star fields and greater separation of nebulae.

Overall, really happy with the quality and look forward to getting the Oiii and Sii

Rating (max 5):  
17 November 2019  | 

Can't believe how much difference makes the Ha filter.
I captured stunning data even during full moon! Light pollution? No problem!
Added some Ha data to my old images shot with stock Canon DSLR and I was really impressed by the results.
Didn't have any problem finding focus with my SW ED80 and ZWO 1600MM Pro - just pick a bright star, increase the gain and you will easily find the perfect focus with a Bahtinov mask (even at 300ms!)

Rating (max 5):  
Try one of these with Night Vision...
29 April 2018  | 

Using this fine filter with military night vision enables ha nebulas not visible to become visible. It's like magic!


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