Starscapes at Sunset Crater National Monument – FEB 13, 2010

Orion, Canis Major, and the Winter Milky Way soar over Sunset Crater

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FEB 13, 2010 – 01:00 AM MST
Canon EOS 300D + Kit Lens @ 21 mm • ISO 800 • f/4.5
Composite: 11 x 30 sec. aligned, stacked, and composited separately for sky and foreground

I said I was going to try this again. Things worked a little better this time (including remembering to check my ISO setting). I arrived early (12:30 AM 🙂 at Cinder Hills Overlook to work on an observation and sketch of Messier 101. Orion and Sirius would be in good position over Sunset Crater between 12:30 and 1:30 AM. After getting the series of shots I wanted, I couldn’t resist shooting another set to the northwest showing Orion, the Hyades, and the Pleiades all setting behind the hills and trees.

Mars, Procyon, and Sirius line up over Sunset Crater

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FEB 13, 2010 – 01:00 AM MST
Canon EOS 300D + Kit Lens @ 21 mm • ISO 800 • f/4.5
Composite: 6 x 30 sec. aligned, stacked, and composited separately for sky and foreground

I got three shots into that series before Rigel winked out behind the mountain. At that point, I noticed that Sirius, Procyon and Mars were making a brilliant alignment over the peak of the volcano. So I worked on a vertical series to capture them.

Mars, Procyon, and Sirius line up over Sunset Crater

Click for larger image
FEB 13, 2010 – 01:00 AM MST
Canon EOS 300D + Kit Lens @ 21 mm • ISO 800 • f/4.5
Composite: 6 x 30 sec. aligned, stacked, and composited separately for sky and foreground

Shooting 30 second tripod exposures makes random course-corrections pretty simple…perhaps too simple.

Processing one set of images is hard enough. Adding a second and third gave me a workout. It was a much needed workout too, since it forced me to refine my process. I made some improvements on the second image, and then again on the third image. By that time, I felt I had to go back and re-do the first and second again.

I’ve felt pretty confident handling stacking and compositing for sky and foreground. The processes I find challenging are:

1. Removing green/red blotchiness from the dark sky background
2. Removing just the right amount of noise without making the sky look plastic or crystalized
3. Reducing the appearance of vertical and horizontal bands in these short exposures.
4. Tamping down light pollution gradients with some level of finesse

Briefly, some of the solutions I arrived at:

1. To color balance the background, I create a temporary layer, blur it extremely, and read RGB values in different parts of the sky that aren’t hit hard by light pollution or air glow on the horizon. I then apply a curves adjustment layer to balance the background to an average of neutral. Unfortunately, that doesn’t remove the color blotches. So I add a Hue/Saturation adjustment layer to substantially reduce saturation, and then use Astronomy Tools “Select Bright Stars” to create a mask for this layer that blocks out the stars, and leaves their color intact. Unfortunately, this removes the ability to feature any photographic color in the Milky Way, but for the type of color noise I have to deal with in these 30 second exposures, I think it’s a good sacrifice. I also like the way it better conveys the more neutral visual experience of the sky.
2. I use Neat Image to tackle noise. Wide field images like this tend not to have decent sized empty areas that the software can sample for average noise. As a result I have to play with the settings over and over again to get what I like. I still don’t have a good system here. Just experimentation. I’ve saved my latest setting in hopes that I can use it again, but I have a feeling I’ll still have to fiddle with it quite a bit every time.
3. The Astronomy Tools “Horizontal/Vertical Banding Noise Removal” action really does a great job removing much of the banding. However I’ve got some pretty huge bands in these frames, and it doesn’t remove those. Wherever these hit a soft hint of Milky Way, they become impossible to remove. A new camera may eventually help this situation 🙂
4. A couple of the shots contained a pretty ripe light pollution tongue that tore right into the Milky Way. It doesn’t seem that obnoxious visually, so I did want to tame it a bit. I found that examining the individual color channels tended to give me some options. The green channel is the cleanest representation of the sky, but the blue channel hides the light pollution the best…the blue channel also seems to do a nice job of giving star groupings and the brightest blue stars a nice glow. I can do some channel blending operations to merge the best of these two channels to create a “Luminosity” layer. By setting this layer to Luminosity mode, I can trim the light pollution, bring out the Milky Way a little more, and in an added bonus, it blunts the horizontal/vertical banding a bit more if I’m careful how I blend blue and green (the blue usually has much worse banding than green). Adding a Hue/Saturation adjustment layer that subtly reduces the intensity of the yellow in shadow and midtones (to exclude stars) helps too.

I’ve still got a lot of improvement to do, but with the system I’ve scripted out, I have high hopes it will go smoother on my next attempts.