524: Photographing the Stars, with Andrew Burwell

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This was a fascinating discussion. Amazing all the work that goes into producing these images. The one question I walked away with, especially when he was discussing the Hubble Palette, is whether these astro-photographs result in an image that is faithful to what you would see with the naked eye from earth or if you were looking out a window of a spaceship passing by one of these celestial objects. (By “faithful,” I’m not applying any kind of judgment. It’s the best word that I could come up with.)

Thanks for this marvellous episode. I have recently taken a deeper dive into astrophotography and Andrew’s MacObservatory site has been enormously helpful. Although there are several astrophotographers on YouTube, Windows software is often an integral part of their workflows. Here Mac-using Dylan O’Donnell explains how he gets around this using Parallels: https://www.youtube.com/watch?v=BFMCYLe1C8E, but I have managed to get started without Windows using Andrew’s suggestions.

Although I enjoyed this episode, I found the order perplexing - ordered in terms of equipment rather than the workflow. If you are starting out, you will need to take things in order, from habit forming and learning new skills to capturing to processing, and along the way considering each new piece of gear you need to take each next step. I’ll share my recent experience and would welcome any comments from others who have tried this or are interested.

I was already equipped with tripod, DSLR, telephoto lens and manual remote control, and had captured solar and lunar eclipses. My husband was interested in a telescope for visual astronomy rather than photography. The thing is, your eyes can’t take a long exposure, or post process images! The first thing I tried was taking photos of the Orion Nebula and the Pleiades with my existing equipment, no star tracker. I was surprised that the Orion Nebula was visible in the electronic viewfinder and managed to get enough shots to align manually and stack in Photoshop and get a slightly better image than any of the individual shots.

We spent a long time considering different telescopes and mounts, and eventually concluded that getting a star tracker was going to be the piece of gear that would make the most difference, allowing for longer exposures. We chose the Sky Watcher Star Adventurer. We also got a much sturdier tripod than the MeFoto that I’m using for photography. It’s really for a Celestron telescope which we plan to get later. For now, the Star Adventurer can mount to one of the 3 screws on top of the tripod, and if we travel for astrophotography I mmay get something more portable but heavier than the MeFoto.

We also got red headlamps - inexpensive but essential to preserve your night vision while out in the dark.

Next, you have to plan your life around the sky. The app you need for this is Clear Outside, which will tell you if there is going to be a clear night up to a week in advance, and will also tell you if this will be made difficult by the moon phase. Its negative reviews are from people who want it to have a fahrenheit temperature option. It doesn’t. I switched my phone to centigrade, and mentally convert to fahrenheit when discussing the weather with fahrenheiters.

It’s good to be flexible. If there’s a bright moon, shoot that instead of fretting that the stars are washed out. If it’s too cloudy for astrophotograpy, there might be a good sunset and the Clear Outside app will help you learn to predict those as well.

Next step is to figure out where you can actually set up. At least with a simple star tracker, you need to be able to align it to one of the celestial poles. Most of the sky where I live is filled with huge trees, but there’s a place where I can see Polaris and there’s also a bit of clear sky to the south as well as overhead. The star tracker’s alignment instructions assume you know the time, your lat long and your position within your time zone. Instead you can use the iOS Polar Scope Align app, which gets time and location from your phone, to precisely align your star tracker. The better you do this, the longer exposure you can take; at least 30 seconds but perhaps as long as 2 minutes. For longer exposures, autoguiding is needed and the Star Adventurer has a port that can be connected to a guiding system, as described in the podcast.

It takes practice to be able to polar align accurately and efficiently, and then not spoil the alignment by moving something. The Star Adventurer isn’t a goto system, so you have to know your way around the sky or use Star Walk or similar to find your target and then learn to get the camera pointed in that direction by rotating the mount. Although you can put a ball head on a star tracker allowing free movement of the camera, its extra weight may make it harder or impossible to balance with the star tracker’s counterweight.

Another issue is focusing your camera. Autofocus won’t work because there isn’t enough light for your camera to work on. Many lenses focus past infinity, so just turning the lens to the infinity symbol won’t do. With the heaviest tripod, touching the camera at all will still make it wobble, so each time you move the focus ring you have to wait for the wobble to stop and then compare with the previous setting. It’s good to use the electronic viewfinder, turned out to a convenient angle and zoomed in all the way.

Another practical note: you’re outside at midnight, it’s below freezing, so your face is covered, you’re using your iPhone for polar alignment and it’s continually locking and needing to be unlocked with face ID, which doesn’t work with your face covered. There’s a watch version of the PS Align app but it takes interaction to make it update.

At this point I was able to take several exposures of the Orion Nebula and align and stack them using Astro Pixel Processor. This is a paid Mac app but has a free trial. The Windows equivalent is free.

I used Photoshop to “stretch” the image; there are tutorials on YouTube and AstroBackyard (https://astrobackyard.com/tutorials/astrophotography-tutorial-1/ ).

After this first experience, I wanted to automate the capture process, and considered: driving the camera remotely using WiFi and camera’s iOS app (apparently unreliable); using a wired intervalometer (reliable but not very remote); using a wireless intervalometer (also unreliable according to reviews). Instead of any of these, my next piece of gear was a very long active USB cable used with the AstroDSLR app on my Mac. I was able to put the cable through a door and both focus and drive the camera from the warmth of my living room.

2 months on, the sky has moved and Orion no longer appears in the clear patch between the trees, so my next step is to find different targets to photograph, or somewhere else to set up. All in all, it’s surprising to see how much you can do with normal photography equipment plus a basic star tracker.


I’d say it’s not for two reasons. H alpha and SII are both red, OIII is green. However the Hubble palette maps H alpha to green and OIII to blue. Secondly, your eyes can’t integrate a long exposure. This article explains and shows examples of different mappings: https://starizona.com/tutorial/narrowband-imaging/

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Wow!! This is great. Thank you.

Really enjoyed this episode. At first I was ready to ignore it thinking the guest was a celebrity photographer. Was pleasantly surprised that it was about actual stars, etc. It combined several of my interests with Mac + Space + Photography.

And speaking of that, here’s a backyard photo of Orion that I took with my iPhone just a few days ago: