This Astronomik H-alpha 12nm 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 an contrast boost, as all unwanted light from other wavelengths than 656nm is blocked form UV up to the IR. This results in an very dark background compared with any filters with a higher bandwidth
The FWHm of 12nm 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 fluy 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!
Astronomik MFR Narrowband-Emissionline Filters (OIII, SII, H-alpha, H-beta)
The new series of Astronomik MFR Narrowband-Emissionline Filters is perfectly matched to the requirements of astronomical Deep-Sky imaging. For the three most important emission lines of Oxygen (OIII), Hydrogen (H-alpha) and Sulfur (SII) you may select your filters either with 12nm or now a very narrow 6nm bandwidth. Astronomik utilises a completely new manufacturing process providing the best Off-Band blocking possible across the entire range of wavelengths from the UV through to IR! The benefit of this new design will be immediately obvious in your images – extremely high contrast, minimized stray light, no halos and needle-sharp stars.
Should I choose a 6nm or 12nm filter?
- 6nm filters are the perfect choice for capturing delicate detail in heavily light polluted skies. They are also appropriate with sensitive, low noise cameras under dark skies and for imaging faint detail in objects surrounded by rich star fields – and hence prone to overly saturated stars in the image. Best with f/3.75 to f/15 telescopes.
- 12nm filters are for photographers using typical DSLR cameras, inexpensive One Shot Colour CCD cameras or “noise limited” devices. The wider 12nm bandpass filters are also preferred generally when using cameras with an integrated guiding chip (behind the filters). Far fewer guide stars will be available at 6nm compared to 12nm. Best with f/2.8 telescopes and up.
What if my telescope has a fast f/ratio?
Unlike filters from many manufacturers, the transmission curve of the new Astronomik Narrowband-Emissionline filters are essentially free from bandpass shift when used with fast optical systems! While other manufacturers may sell special “High Speed” filters, or even require you having to buy different filters for each scope, this is not the case with the new Astronomik Narrowband-Emissionline filters with MFR coating. Your 6nm filters will be hunky dory on any telescope down as fast as f/4! (or f/3 with the 12nm FWHM filters).
How do I choose between OIII, SII, H-alpha, and H-beta?
The H-alpha filter is recommended as the filter of choice to begin exploring this amazing field of astrophotography. With a Narrowband 6nm 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! A quick look at beautiful astrophotos will show an H-alpha filter is the best choice for all nebulae glowing with hues of pink to red. Think Orion Nebula, Eta Carina Nebula, Lagoon Nebula, Swan Nebula and so on and so forth. H-alpha light also appears in deep images of galaxies with active star formation regions showing up as beautiful pink knots in the spiral arms. In short – if you’re not incorporating H-alpha data into your images you must be bonkers.
An OIII filter (doubly ionized Oxygen) expands your imaging possibilities, as you are able to image all greenish/blueish structures. Planetary nebulas and star forming regions are great targets!
An SII filter (ionized sulphur – deeeeep in the red) completes your HSO set. With these three filters you are able to process your images like the ones from the Hubble space telescope (allowing compensation for atmospheric, or human-based error of course!).
The H-beta filter is not available in a 6nm version, as this filter has nearly no meaningful application. Used for very specific imaging targets such as the California Nebula, Horsehead Nebula, and some assorted planetary nebulas. Not recommended for beginners, and generally not widely used by most astronomers.