This was shot with a Rokinon 135mm telephoto over several nights in the Anza-Borrego desert. It was shot using LRGB wideband filters and Ha narrowband. The Ha was mixed into the red channel via continuum subtraction using Adam Block's NBColourMapper script and technique.
Light pollution in the form of passing satellites was a serious problem with this object. I shot 156 3-minute wideband subs and every single sub had at least one satellite trail and some had many. Most of the trails fell along a radiant line under the Witch's chin. Standard statistical data rejection techniques (WBPP) did not completely mitigate the problem so some of this had to be corrected in the integrated images. I made a video of all of the 156 subs, so interested parties can see the issue here:
https://vimeo.com/896382905The spikes in the stars are due to the aperture blades in the telephoto (shot at f4 rather than the wide open f2 aperture). I experimented with smoothing out the spikes in the stars and decided I liked the original with the spikes the best. I also experimented with diminishing the stars to bring out the nebula, but decided that the stars added a lot to the image.
Despite the ~90 million light-years distance between Rigel and the Witch Head nebula, the light illuminating the Witch Head is in fact from Rigel and shares the same spectral qualities. Most of the red in the image is due to ionized gas emitting Ha.
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