Orion in Hydrogen Alpha

6 February 2019

We don’t have an image of the week going here, but occasionally we see photos that are something special. Tony Cordaro posted this on the Australian Amateur Astrophotography Facebook page the other day.


This is a stack of 15 five minute exposures, shot through an Astrodon Hydrogen Alpha (Ha) filter. The camera is a cooled monochrome astronomic CCD behind a Samyang 135mm lens at F3. All the subframes are unguided, so polar alignment was critical.

I do have a personal failing for Ha photographs, not only because I’m of an age where I remember processing my own black and white film, but also the aesthetics. Also, I happen to think that the Orion area is about the coolest emissions anywhere, apart from NGC 6188.

Ha photos have a particular sharpness to them, as the narrowband filter rejects other spurious frequencies enabling a razor-sharp focus that highlights all the swirls and mystery of the nebulas.

The field covers everything from the Great Nebula (M42), through the Running Man, de Mairan's Nebula, the Horsehead to the Flame Nebula. That's a huge field in anyone's book.

Tony says that he still wants another 4-6 hours of Ha data on top of this, and he’ll add other couple of narrowband filters to complete a full false colour image.

Great work, Tony!