This H-alpha 12nm CCD-Filter is suitable for imaging of Hydrogen nebulas from observation sites with light pollution and from dark sites as well. The contrast between an object glowing at 656nm and the background is increased enormous!
Due to the combination of the narrow bandwidth of 12nm and the high transmission of typically 96% the filter gives you a contrast boost, as all unwanted light from other wavelengths than 656nm is blocked from UV up to the IR. This results in a very dark background compared with any filters with a higher bandwidth
The FWHm of the H-alpha 12nm CCD-Filter 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 flux 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 6nm 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.
Imaging with Narrowband-Emissionline Filters
If you have to observe from light polluted sites (like most of us…), imaging with Narrowband-Emissionline filters is the best way to take great images, as all kinds 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 a 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 expands your imaging possibilities, as you are able to image all greenish/blueish structures. Planetary nebulas and star-forming regions are great targets! The SII filters 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!
The h-beta filter is not available in a 6nm version, as this filter has nearly no meaningful application. To illustrate this, there are two images shown below: Both were taken with an unmodified Canon 650D. Even as the camera has a sensitivity of less than 10% at H-alpha, there is some signal and structure in the h-alpha image, while you cannot see anything on the image taken with an H-beta filter!
Operation of the filter:
The filter blocks all unwanted light from artificial light-pollution, natural airglow, and moonlight. Especially light from High- and Low-Pressure Sodium and mercury lights and 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 656nm.
Tipps 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
If want to image faint objects in star crowded regions of the Milky Way, probably using short focal lengths, the 6nm filter will be the better choice, as the number of stars is reduced by a factor of ~2. You should even take the 6n inversion if you have a camera with a low thermal current or if you have to observe from a really heavily light-polluted site.