Weekend Amateur: Learning from an astrophotography mistake

The Weekend Amateur documents my personal exploration of outer space where I dabble with the different aspects of amateur space exploration. 

Peering through alleys of dust into the heart of the Milky Way. (Image: Chris Casper)

Peering through alleys of dust into the heart of the Milky Way. (Image: Chris Casper)

I’m dabbling with astrophotography. (Any serious amateur is cringing right now) This picture turned out fairly well given the light pollution in Southern California - and the street lamp next to my condo’s balcony. It might have been a better picture if I had aimed the camera at the right place. Star-hopping through a DSLR’s viewfinder isn’t easy. Of course, mistakes give us the chance to learn…. 

I learn a lot.

I must have nudged the camera upwards a tad. Rather than the constellation Sagittarius, I took a picture of the gap between the constellations Sagittarius, Ophiuchus, Serpens, and Scutum. A lot of interesting things lie in that gap. We’re looking through the Milky Way’s spiral arms towards the galactic core. The mottled appearance and the dark bands on the left hand side are dark nebulae - giant molecular clouds of gas and dust where new stars are born. The two bright spots below the center are nebulae - Messier 16 (the Eagle Nebula) and below that the somewhat closer Messier 17 (known as the Omega Nebula among other names) - two star-forming regions where young stars emerge from their surrounding dust clouds. Below that is a white patch of stars, Messier 24, which isn’t a real structure at all. We are looking through a tunnel in the dust clouds towards the galactic core. Over to the right is a star cluster, Messier 23, which lies about halfway between the Sun and the Omega Nebula. 

One of twelve exposures used to create the image.

One of twelve exposures used to create the image.

It’s been about two weeks since I took the original pictures. I’ve been figuring out In stops and starts how to process the images into something useful. Here’s what one of the pictures looked like straight out of the camera:

I can’t claim that this is a technically excellent image. I need to work on the technical aspects of setting up the camera and processing the images. More importantly I need a more intentional approach. Understanding what am I trying to show - whether the pervasiveness of dust clouds or the star-forming activity in the nebulae - will let me make better decisions up front so I don’t need to do as much work in post.

I’m concentrating on technique because astrophotography can easily turn into an expensive rabbit hole of technology upgrades. My goal is to figure out how to make the best images I can with the stuff I already own. Two concessions to the tech gods was my purchase of Vixen’s Polarie Star Tracker and an Orion 90mm tabletop telescope. The Polarie moves the camera in time with Earth’s rotation so the stars don’t move during the long exposures. 

Long being a relative term. Professional astronomers design their observatories with such precision that their telescopes can track an object for hours. Most amateurs don’t have that luxury, but they can adopt  professional techniques to blend several short exposures together. That process reduces any noise generated by the sensor while increasing the contrast between the stars and the background. In this case I took twelve twenty-second exposures. An even dozen seemed like a nice number. I wanted to make sure the stars weren’t blurred. Twenty seconds guaranteed it. As I get better at this I will run longer exposures. 

Keeping with the theme of using what I already have, I did the post-processing work in Adobe’s Lightroom and Photoshop. After some experimentation, I found a process that seems to work. I brought the files into Lightroom and made global adjustments to white balance, exposure, and contrast. This created enough separation between the stars and the background for Photoshop’s auto-alignment function to work. Then it’s just a matter of using Photoshop’s stacking and flattening tools to combine the twelve images into a single file. Back to Lightroom where some tweaking and local enhancements produced the final image.

There are several dedicated astronomy apps that can do this more efficiently. Most of the inexpensive software is written for Windows which my Mac won’t run. Astronomy-focused variations of the free image processing app ImageJ will run on the Mac, but I couldn’t find ways to use AstroImageJ or SalsaJ with RAW files from my DSLR. 

A project for another time.