This H-alpha EOS R XL clip-in Filter is suitable for imaging of Hydrogen nebulas from observation sites with light pollution as well as from dark sites. When using this filter, the contrast is greatly increased between an object glowing at 656 nm and the background.
Due to the combination of the narrow bandwidth of 12 nm and the high transmission of typically 96% this filter gives you an contrast boost, as all unwanted light from wavelengths other than 656 nm is blocked form UV up to the IR line. This results in a very dark background compared with filters with a higher bandwidth.
The FWHM of 12 nm is optimized for typical DSLR cameras with CMOS sensors and CCD cameras with a normal/high dark current. With these cameras the background signal in images taken from heavily light polluted sites is dominated by the dark current of the sensor, not by stray light signals coming from light pollution. In this case a further reduction of FWHM does not improve the image, as the background will not get darker.
Compared to the 6 nm filters you have more stars in the field of view which gives you more guiding stars when working with an integrated/dual guiding chip.
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!
Technical data of the filter:
- 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): 12 nm.
- 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 1 mm.
- Not sensitive to moisture, scratch resistant, not aging.
- Optically polished substrate, mark-free, and free of residual stresses.
- High quality storage box.
Imaging with Narrowband-Emission line Filters
If you have to observe from light polluted sites (like most of us...), imaging with Narrowband-Emission line filters is the best way to take great images, as all kind of light pollution can be blocked very effectively. 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 astrophotos, an H-alpha is the best choice for all nebulas glowing red! An OIII filter will expand your imaging possibilities, as you are able to image all greenish/blueish structures. Planetary nebulas and star forming regions are great targets! A SII filter will complete your HSO-set of filters. With these three filters you are able to process your images like the ones from the Hubble space telescope! An H-beta filter is not available in the 6 nm version.
Operation of the filter:
This filter blocks all unwanted light from artificial light-pollution, natural airglow, and moonlight. Most notably, is will block light from High- and Low-Pressure Sodium and mercury lights. 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 656 nm.
Tips and Hints for more applications:
Using the H-alpha filter together with OIII-CCD and SII-CCD filters you make produce false-color emission line images (HSO) in the same way as the Hubble-Space telescope. This is possible even from heavily light polluted sites.
Alternatives: If want to image faint objects in star-crowded regions of The Milky Way, (probably using short focal lengths,) the 6 nm filter will be the better choice, as the number of stars is reduced by a factor of ~2. You should even take the 6 nm version if you have a camera with a low thermal current or if you have to observe from a really heavily light polluted site.