Astronomik H-alpha 6nm Filter

Astronomik H-alpha 6nm Filter 1,25" (M28.5)

Astronomik H-alpha 6nm Filter 1,25" (M28.5)
Astronomik H-alpha 6nm Filter 2" (E48)
Astronomik H-alpha 6nm Filter 31mm, unmounted
Astronomik H-alpha 6nm Filter 36mm, unmounted
Astronomik H-alpha 6nm Filter 38mm, unmounted
Astronomik H-alpha 6nm Filter 50mm, unmounted
Astronomik CLS EOS Clip-Filter
Astronomik H-alpha 6nm Filter SC Rear Cell (2" / 24TPI)
Astronomik H-alpha 6nm Filter T-Mount (M42x0,75)
Astronomik H-alpha 6nm Filter Transmission Curve

Click the image for full resolution

The Astronomik 6nm H-alpha filter is an extremely narrow emission-line filter for CCD photography. The filter lets the H-alpha light of emission nebulae pass and blocks nearly the whole remainder of the spectrum where the CCD is sensitive.

The full width at half-maximum (FWHM) of 6nm is optimized for a maximum contrast between the (H-alpha emitting) object and the background. The contrast gain is much higher than with our 12nm emission line filters but you won’t see as much stars in the resulting images.

The design of the transmission curve makes it possible to use the filters with instruments from 1:3.75 to 1:15. Selected filters for faster system are available upon special request.

All transmission curves of the 6nm filter are measured individually. Because of this procedure you can get the optimum filter for your telescope: If you place a direct order please specify the focal ratio of your instrument and we will select the best filter for your setup. So you may get the best filter without paying for an A+ filter.

Main use

The Astronomik H-alpha-CCD (6nm version) increases the contrast between objects, in this case between the H-alpha emission line and the skyglow background in the same way as the 12nm version. The gain in contrast is much higher due to the smaller FWHM. The 6nm H-Alpha filter is the right choice for extremely dim objects, even in the milkyway, and for observations from heavily light-polluted places. The Astronomik 6nm H-alpha-CCD completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow. Transmission losses and chromatic distortions, which arise with other filters, only occur with Astronomik filters when extremely bright aperture ratios come into play. Selected filters for faster systems are available upon special request.

Other uses

  • Using the Astronomik 6nm H-Alpha together with the 12nm H-Alpha gives you the ability to have a maximum contrast in the HII objects and to keep the stars in the final image.
  • The Astronomik 6nm H-Alpha filter may NOT be used for solar observation.


If you plan to do (false-)color imaging with other emission line filters, you should get our filters with 12nm FWHM. Images taken with filters with differing FWHM are very difficult to combine into the final image.

more information about the photographic Astronomik filters

Transmission curve
Transmission curve
How to read the 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 red line shows the transmission of the filter.
  • Visual filters: The grey line in the background shows the relative sensitivity of the human eye at night. The maximum is at ~510nm and drops to longer and shorter wavelengths. You can easily see, that you can´t see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity at 656nm is 0% at night!
  • Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.
  • The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by see mercury (Hg) and sodium (Na), which are used in nearly all streetlights.
  • The most important emission lines from nebulas are shown in green. The most important lines are from ionized Hydrogen (H-alpha and H-beta) and double ionized oyxgen (OIII).

The major emission lines of artifical 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


  • Visual observation (dark skies): Unsuitable
  • Visual observation (urban skies): Unsuitable
  • Film photography: Unsuitable
  • CCD photography: Very good, huge contrast enhancement at H II-emission nebulas
  • DSLR photography (original): Good, reduced sensitivity in the H-alpha band
  • DSLR photography (astro modified): Very good, huge contrast enhancement at H II-emission nebulas
  • DSLR photography (MC modified): Very good, huge contrast enhancement at H II-emission nebulas
  • Webcam / Video (Planets): Unsuitable
  • Webcam / Video (Deep Sky): Unsuitable

Technical Data

  • typ. transmission von über 90% at H-Alpha (656nm)
  • Parfocal with other Astronomik filters
  • Glass thickness: 1mm
  • Completely resistant against high humidity, scratches and aging effects
  • Diffraction limited, the filter will not reduce the optical performance of your telescope!
  • Astronomik filters are delivered in a high-quality, long lasting, filter box
  • Since 2008 we do ship filters with a completely new design. Any kind of halo or strange reflection is a matter of past

The filter is available in the following sizes:

H-alpha 6nm CCD-Filter

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