Astronomik 2-Inch H-Alpha 12nm Passband Filter for CCD Photography
Mounted filter in 2" cell ( M48.5mm x 0.75mm)

The Astronomik H-alpha 12nm filter is a narrow band 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.

Astronomik have re-designed all of their photographic filters. Since the end of 2008 they are shipping their new "Halo-Free" filters.

The full width at half-maximum (FWHM) of 12nm is optimized for the use with common CCD cameras and allows the use of very fast optics. It should be noted that the filter has a transmission of up to 99%.

Another advantage of the 12nm filters is the availability of guiding stars for cameras with a built-in-autoguider (SBIG). If you use a very strong filter like our 6nm filter you often won’t find a usable guidestar.

The range of application extends from 1:2.8 to 1:15. Transmission losses and chromatic distortions, which arise with other filters, only occur with Astronomik filters when extremely bright aperture ratios of 1:2 and more come into play.
 

Main use

The Astronomik H-alpha-CCD (12nm version) increases the contrast between objects, in this case between the H-alpha emission line and the skyglow background. Our Astronomik H-alpha-CCD (12nm version) completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow.

Other uses

• When using the OIII CCD and the SII-CCD filters you can obtain three-color images of emission line objects (gas nebulae) from locations with very strong light pollution. To do so, you would take an image in three different wavelengths, select each one as a color-channel in Photoshop and paste them together as a color image.
• The Astronomik 6nm H-Alpha filter may NOT be used for solar observation.
• If you plan to create color images from emission line data, our CLS-CCD filter is a great choice for the Luminance channel.

Suitability

• Visual observation (dark skies): Unsuitable
• Visual observation (urban skies): Unsuitable
• Film photography: Reasonable, but very long exposure times
• CCD photography: Very good, huge contrast enhancement at H II-emission nebulas
• 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
• DSLR photography (original): Good, reduced sensitivity in the H-alpha band Webcam / Video (Planets): Unsuitable
• Webcam / Video (Deep Sky): Good, good contrast enhancement with bright objects

Technical Data

• Transmission of over 97% with the H-alpha line (656nm)
• Complete blocking from all disturbing wavelengths in the infrared
• 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

How to read the above 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 filled with grey  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 of the eye 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 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 most important artifical emission lines are shown in orange. The artifical light pollution is dominated by mercury (Hg) and sodium (Na), which are used in nearly all streetlights.
   

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