Astrophotography and Teaching

I have been interested in photography for years. I have a good understanding of composition, the exposure triangle, depth of field, and many other photographic concepts as well as how to choose lenses and manipulate the settings of my various cameras to make photos that I find interesting. For the last three plus years (today is day 1215), I have engaged in a daily photo project that has taught me how to really look at ordinary things as well as how valuable consistent engagement is for improving skills. I try to challenge myself every day with this project but I was starting to feel like I wasn’t learning a whole lot of new lessons related to photography. So I decided to try my hand at astrophotography. I am learning lots of new lessons about photography but I am really surprised about how much I’m learning about teaching by engaging in this new hobby.

Astrophotography involves making photos of celestial objects and phenomena. Celestial objects are things like the moon, the planets, the Milky Way, stars, galaxies, comets, and satellites. Celestial phenomena are things like phases of the moon, one celestial body eclipsing another, meteor showers, and planetary alignments. Photographing these objects and phenomena is more challenging than photographing nearly any other object. They are typically dim and far away and, therefore, they emit little light. Photography is all about capturing light on film or on a sensor. So dim, far-away things are a particular challenge to photograph. The amount of light we capture depends on 3 things (the exposure triangle): ISO (how sensitive the film or sensor is to light), aperture (how wide open the shutter is), and exposure time (how long the shutter is left open). To capture enough light to be able to see details of celestial objects and phenomena, we often we need to use very high ISOs which introduces noise or graininess into the image and/or we have to use very large apertures which means we have a very narrow window of focus and/or we have to use very long exposure times (slow shutter speeds) which introduces the possibility of undesired movement in either our subject or our camera causing blurriness. This exposure triangle is something we have to deal with in other kinds of photography as well but we can often make very good photographs even if we make small mistakes. Astrophotography is much less forgiving. And so there are a lot of tools available to minimize those mistakes. And lots of tips about how to use these tools effectively. This makes the astrophotography learning curve long and pretty steep. I’ll stop trying to convince you that astrophotography is different than other kinds of photography. Just know that it is and I have a lot to learn.

When I decided a couple of months ago that I wanted to venture into this new kind of photography, I started reading some blogs posts and watching some videos about how to get started using the equipment that I own. The problem that I ran into was that the advice was scattered and overwhelming and not all of it seemed to apply to my particular situation. There was no consistency and I couldn’t find an easy path to my first step. So I decided to buy a book. Retro, I know. I bought Digital SLR Astrophotography by Michael A. Covington. From this experience, I (re)learned the lesson that we need to provide on-ramps to new knowledge for our students. How can we help them make sense of the mass of new content and skills that we are trying to teach them? How can we help them to build mental models that connect the content and skills we’re teaching with what they already know?

From the Covington book, I learned some basics. For example, I learned the difference between a star tracker and an equatorial mount and since I don’t have either, I learned that to estimate the longest shutter speed I can use without starting to get unwanted star trails as a result of the rotation of the earth, divide 500 by the focal length of my lens. With my newly acquired knowledge, I felt pretty confident that I could go out and make some photos of easy targets. I decided to start with my 50mm lens to make a photo of the Big Dipper. Since the focal length of my lens is 50mm, I knew that my shutter speed could be no slower than 10 seconds (500/50mm=10 seconds). I made this image of the Big Dipper and am really happy with it. The stars don’t have trails and there is no noise in the background. And this photo got me really excited to target something a bit more difficult. This is the second lesson I learned. It’s important to provide opportunities for some early, not-too-easy successes so that students are challenged and excited rather than frustrated and discouraged.

As my next, more difficult astrophotography target, I chose Saturn. I had seen a lot of photos made by amateurs that showed amazing detail in the rings around the planet. I pointed my 50mm lens toward the planet and made an image that showed Saturn as a small dot. I knew from the Covington book that I could use various kinds of image processing software to try to pull details out of that small dot, to try to make the rings and other planetary details visible. This post-processing is something that I am working on but I thought I might be able to get more detail in the unprocessed image if I used a bigger lens (more magnification). So I switched to my 100mm lens and made the following image.

This image has the kind of trail that I was talking about earlier in this post. When I made the image, I kept my shutter speed at 10 seconds which I had used with my 50mm lens. But the 500 rule says that the slowest shutter speed I can use with a 100mm lens is 5 seconds (500/100mm=5 seconds) in order to avoid capturing the rotation of the earth in relation to the celestial objects. I knew this rule but in the excitement of making an image of a new target, I forgot it. I think there are two lessons here: 1. Having already “covered” material doesn’t mean that students have internalized it to the point where they won’t forget it; and, 2. it’s important for students to be able to see their mistakes for themselves. How can we help students internalize the content and skills from our classes? How can we make mistakes visible to our not-yet-expert students so they can find the mistakes themselves?

I then set the shutter speed to the correct 5 seconds but I still couldn’t seem to get a clear image of Saturn. So I decided to try to recreate my successful image of a constellation using this lens. I targeted Cassiopeia and made the following image. Notice how strange the stars look. Nothing I did seemed to fix those stars.

One of the resources I had discovered before I bought the Covington book was a Facebook group devoted to learning astrophotography. I had lurked there for a while and learned a lot from the images members posted and the feedback from other members. Because I had exhausted all of my ideas about what was wrong with my photo of Cassiopeia, I decided to ask for ideas in this group. Although I am a confident learner, I was nervous about putting my mistakes out in front of others who are learning astrophotography. My lesson here is that it is scary to make yourself vulnerable by admitting what you don’t know in communities where you haven’t yet built trust. How can we help students to trust not just us as the instructor but also the other students in the class so that they are willing to ask questions about what they don’t know?

I posted my photo along with a question about what might be going wrong in the photo. The responses started within minutes. The first several just said “focus.” This was not a particularly helpful response because I had set the focus on my lens to infinity which should mean any stars would be in focus. This made me think about the feedback I give to my students on their work. Feedback should be clear, constructive, and actionable. In other words, feedback should be more than a single word. It should contain an explanation of what is wrong and, most importantly, how to fix it. One of the responses I received said, “Obviously, the problem is focus.” The word “obviously” is problematic here. If the answer was obvious, I wouldn’t have asked the question. To a beginner, nothing is obvious. Feedback should not make students feel badly about asking their question. No matter how many times you have received this question, it is the first time the student has asked it. At this point, I thought about removing my question because it felt like an embarrassing mistake. How could I not have focused the image? Stupid, right? But then I started to get responses that made it clear that focusing dark images like this is really challenging. The best responses gave me specific things I could do and/or think about when focusing. For example, one person told me that focusing on infinity is rarely achieved by moving the lens to what feels like infinity. Sure enough–when I tried focusing on infinity in the daylight with this lens, the best results came just before I thought I was at infinity. In astrophotography, focus is not a “close enough” endeavor. It has to be exact. Another person suggested that I get a bahtinov mask, a simple, cheap tool that I had never heard of, to help with focusing. A third person suggested the thing that I think was causing most of my problem. He asked if I had vibration reduction turned on in either my camera or my lens. I did. Turning this off is critical for astrophotography and I didn’t know that. Feedback should include specific actions to take in order to make improvement. After focusing this lens, I took some photos tonight and the stars in my photos are sharp now. So focus was indeed the issue with my previous attempts. I look forward to trying my newly focused lens on Saturn but there are clouds in the way at the moment. I’m glad that I was able to test out my solutions to the focus problem before conditions were perfect for it. And that’s perhaps the last lesson for this post. Give students lots of opportunities to practice applying content and new skills. Don’t just wait for the perfect condition of an exam.

A follow-up that I’m still trying to process: I got a 24 hour suspension from the learning astrophotography Facebook group after posting my question. First, the post was marked as spam and removed. Then, when I questioned that decision in the group, my new question was deemed unrelated to learning astrophotography (which I agree with) so I was suspended for 24 hours. There is no indication as to why my question regarding the look of the stars in my image was marked as spam. Others must have had this experience recently because one of the admins just posted this:

Just a quick suggestion to those whinging about some members telling other members to google things and the apparent rudeness of not being able to access the answers to some of the questions they ask – but pls be reminded this is an ‘astrophotography’ group. It would be handy to learn a little about telescope operation basics, maybe a bit of visual astronomy or general astronomy and possibly photography before jumping into astrophotography and interacting here in this group. Just a suggestion.

I don’t have an articulate response to this yet. But I’ll just say that “learning” is in the name of the group as well. I’m sure there’s a lesson about teaching here.

The featured image is Jupiter Rising, taken by me on July 27, 2022, with my 50mm lens.