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 the 12nm emission line filters but you won't see as many stars in the resulting image. The design of the transmission curve makes it possible to use these filters with instruments from F1:3.75 to 1:15. Selected filters for even faster systems are available upon special request. All transmission curves of the 6nm filter are measured individually. Each 6nm filter is gauranteed to have a minimum 90% transmission at F4 and each filter has its transmission printed on the box. Typically you will see transmission as high as 96%!
Main Use
The Astronomik H-alpha-CCD (6nm version) increases the contrast significantly 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 H-Alpha objects and to keep the stars in the final image. The Astronomik 6nm H-Alpha filter should NOT be used for solar observation.
Alternatives
If you plan to do (false) colour imaging with other emission line filters, you should use matching filters. i.e. 6nm with other 6nm not 6nm plus 12nm. Images taken with filters with differing FWHM are very difficult to combine into the final image.
Suitability
- Visual observation (dark skies): Unsuitable
- Visual observation (urban skies): Unsuitable
- Film photography: Unsuitable
- CCD photography: Very good, huge contrast enhancement on 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
- 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
