H-alpha photography
I made my first baby steps in H-alpha photography. I bought a 12nm H-alpha clip-in filter for my modified eos 20D camera. The H-alpha filter transmits the wavelength range of hydrogen nebulas (a narrow band around 656 nm) and blocks nearly the whole remaining rest of the spectrum to which CCDs are sensitive. This allows very long subexposures as almost no radiaton from light pollution can reach the sensor.
This works pretty nice. Yesterday I tried a 20 min exposure using my 50mm Canon lens at f/1.8 and this gave a nice view of the Orion constellation and several nebulous areas that emit the characteristic H-alpha wavelength. The drawback of this technique is that it leads to very reddish pictures:
After viewing a few examples, these are not very appealing pictures, and in general one converts these H-alpha pictures to black-and-white which give nice shades of grey. Here is my first result with one 15 min exposure and a 135mm lense:
http://www.astro.pwng.nl/item/rosette-nebula
Another technique that uses H-alpha frames is the so-called HaRGB method. This combines H-alpha frames with one-shot colour RGB frames and this will enhance the contrast and quality of the Red channel.
I will need much more study and experimenting to master this technique. Here is some literature to start with:
http://starizona.com/acb/ccd/software/ps_hargb.aspx
http://www.robgendlerastropics.com/HARGB.html
http://www.robgendlerastropics.com/LRGB.html
http://www.mlunsold.com/process/HaRGBCombine/HaRGB.html
More to follow..