The Astronomik H-alpha 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.
The half width 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%, which cannot be attained by stacking more narrow-band filters. A further note, which led to selecting the half width (FWHM), is the dark current of common CCD imagers. Exposures with a CCD cooled to -15°C are limited by the dark current, even in large cities with a bright background.
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.
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.
- 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.
- Visual observation (dark skies): Unsuitable
- Visual observation (urban skies): Unsuitable
- Film photography: Reasonable, but very long exposure times
- CCD photography: Verry good, huge contrast enhancement at H II-emission nebulas
- DSLR photography (original): Good, reduced sensitivity in the H-alpha band
- DSLR photography (astro modified): Verry good, huge contrast enhancement at H II-emission nebulas
- DSLR photography (MC modified): Verry good, huge contrast enhancement at H II-emission nebulas
- Webcam / Video (Planets): Unsuitable
- Webcam / Video (Deep Sky): Good, good contrast enhancement with bright objects