A weekend soliloquy about night sky photography

I feel like writing a big ol' post about my latest adventures with night sky photography. This will be of interest to only a few, so don't say you weren't warned.

June is a good month for photographing the Milky Way, so after we got back from Paris I decided to give this another go on my next moonless dex night. That was the evening of June 27. I also figured I might as well find the darkest site I possibly could, which turned out to be this one a few miles north of Desert Center:

According to my dark sky map, this is just about the darkest spot in all of Southern California. So off I went.

When I got there, the sky was great. It was clear and dark and beautiful. So I pointed my camera at the core of the Milky Way, took a dozen shots, and then stacked them when I got home. It came out pretty well:

This is about as good as I'll ever get given the limitations of my camera. However, there was also an experiment I wanted to try: I have a filter that allegedly filters out light pollution and I wanted to see how well it works. Here's a side-by-side comparison:

The filtered image is on the right. Toward the horizon it really does filter out some of the crap and add a bit of definition. On the other hand, it also adds a magenta tint and blocks a bit of light. It's something of a wash, I think.

But this is only the beginning of my story. What really drew my attention at the Desert Center site was something else: I could see the entire arch of the Milky Way with my bare eyes. That had never happened before, so naturally I set everything up and started shooting a vast panorama that would capture the entire arch.

It was a disaster. The biggest problem was focusing on infinity. Unlike a fixed length lens where you just set the focus at maximum and snap away, the zoom lens on my camera has a different infinity point at every zoom setting. What's worse, the night sky is too dark for autofocus to work and it's also too dark to see anything. So you have to guess at the correct focus. Here's what that looks like:

Over the years, I have eventually figured out that at 24mm I'm focused at infinity when the right side of the focus point lines up with the decimal point in 0.4. So I snapped away.

But then I tilted the camera up to begin taking the second row of the panorama—and suddenly everything was out of focus. Unfortunately, the only way to find the correct focus point is to (a) blindly adjust the focus, (b) take a picture, and (c) examine it. So that's what I did until I eventually found the sharpest focus point.

But when I panned the camera on the tripod, it went out of focus again. Other times the camera just lost focus for no apparent reason. Long story short, this happened over and over, and then happened again when I tilted the camera up for the third row of the panorama.

When I got home I discovered that most of my frames were poorly focused despite my best efforts, though the frames from the bottom row were OK. But it didn't matter: Photoshop refused to stitch any of them together. This was disaster #2. I tried other stitching software, but no dice. I got nothing for my six hour drive and evening's work.

Well, not nothing. This whole episode took so long that the darkness was fading away by the time I finished up and drove off to take some different pictures. As a result, I took a bunch of pictures at dawn and sunrise that were pretty nice. Here's one of them:

That's the Colorado River Aqueduct underneath a lightening morning sky. The stars are barely visible and the Milky Way is entirely gone.

So did I give up on the whole idea? Of course not! I thought I had figured out the whole focus thing, so a week later I went out again.

It turned out, however, that I hadn't figured out the focus problem. But now I have. It turns out that my camera is nuts: if you tilt it upward the infinity point changes. I can't even begin to make sense of this. But it really seems to be true, and eventually I was able to get sharp images for my entire arch panorama.

But when I got home, I discovered that most of my images exhibited disastrous amounts of motion blur. wtf? I was, of course, using a long exposure time, and 20 seconds is about the longest you can keep the shutter open at 24mm before the rotation of the earth starts to introduce some blur. But I had used 20 seconds the week before with no problem and I was using 20 seconds again. So why the blur? I still don't know the answer.

In any case, this meant that my pictures of the Milky Way core were no good. However, my panorama of the arch was mostly OK and Photoshop even stitched together the bottom row for me. Hooray! Things didn't go so well for the top row, however, since Photoshop had only a bare star field to work with. I eventually coaxed it to do a stitch, which came out wildly warped. So I wildly unwarped it.

I had high hopes that once I had the two rows created, Photoshop would at least stitch those together. But no. So eventually I did it by hand, which is a lousy way to do it. Here's the final image:

All things considered, that's not bad if I'm grading on a curve. But it's not very good either.

Aside from the craziness with focus, the problem is that my camera is just ill-suited for night-sky shooting. It has a small sensor, which means lots of noise. Its sensitivity is mediocre. And it has a minimum zoom of 24mm, which isn't really wide enough for Milky Way photography.¹

It would be fun to try this again with a better camera, but that would cost a fortune to rent and probably wouldn't be worth it. In the meantime, here's a picture of Venus rising above a tree in the Desert Lily Sanctuary.

¹Aside from the focusing problems, a 24mm lens has to be tilted at a very steep angle to get the entire Milky Way arch. At that angle, it's almost impossible to get software to stitch the images together properly.