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Photographing the Milky Way: How I did it.
avatar July 08, 2018 08:26PM
I had my interest sparked in astrophotography about a year ago when I was set up at a rural park, in the dark, waiting on the Aurora Borealis that never happened that night. Being a little bored, I noticed I could just make out the Milky Way in the sky with my eyes. So I did what seemed natural and tried to photograph it. I felt like I had the right gear to get it done, but was not prepared to do this the right way. I set the camera ISO to 800 and thought that would be plenty. I did not want it to look all noisy. I opened the aperture wide to f1.8 and I believe I did a manual bulb setting on shutter. I must have held the shutter open for a minute or more. The best image I got that night is below.

Compared to images I have seen online, that was unimpressive. I started studying the subject and watched a lot of youtube videos. The key is that you cannot keep the shutter open too long or you will get motion blurring from the Earth's rotation. Depending on your lens focal length, it may be as little as 8 seconds or up to 15 or 20 seconds with a very wide angle. That means the ISO must be cranked-up high, and there will be excessive noise more than likely. How is this fixed? We take many exposures of the same scene, then stack it up as layers to blend out the noise and make the apparent brightness increased.

First things first. We need to download some tools. They are all free. Since I have a Windows PC, I cannot use the most mentioned software, Starry Sky Stacker, which is Mac only. I am using Sequator which appears to be an easier to use tool. But it is Windows 64-bit only. I recommend having Google Earth Pro for making a virtual visit to locations, makes scouting easier. Even if you don't want to do the photography, you can do very cool things with it like explore the moon and Mars. It even has a simple sky map. And add to that Stellarium, which is a planetarium for your PC. It is really a tight piece of software that allows you to see the sky for any day at any location on Earth. It is so powerful that some planetariums are using it.

We are looking for a night near a new moon with mostly clear skies to do this. Your preferred weather website will help with that. Now use the map tool from www.lightpollutionmap.info to try to find a location that might be less light polluted than the suburban areas. The map defaults to Europe, but you can navigate worldwide. Unfortunately it is overlaid on Bing maps, not quite as good as Google maps. Use Google Earth Pro to scout out the location better. You can zoom down to ground level, even if there is no street view available. It uses 3D computer game modeling to render the landscape. Buildings and trees will not show, but the terrain will.

So I used more than one light pollution map, and in combination with Google Earth, I selected a park about 44 miles North of home.

Zoomed in on Lake Ennis and John Muir Park with Google Earth Pro.

Now I am at ground level in the parking lot. That flat rectangle is really a park shelter. And there are many trees to see.

Now a unique thing to do with Google Earth Pro is to set the time and have it recreate the sky conditions. I set the time to night. It tries to show where the Milky Way is, but it is actually wrong, by a good bit. Because of this, I did not realize I composed my first photo scene wrong.

What I recommend based on 20/20 hindsight is that you use Stellarium to determine the direction of the Milky Way (or any particular star) at any specific time. The Milky Way moves around and even sets as the night progresses. Stellarium will show that. Bring a compass, and you can do some composing when you have some twilight yet at sunset. I wish I could share screen shots, but the key combo to do that seems to be disabled when running Sample Stellarium screen below. This is powerful software, and if you even get the precise GPS co-ordinates to enter in, there is a way to activate a view that estimates the effects of light pollution on your view. For my hometown, it seems to be close to correct.

So when I arrived at that park at twilight, I set up based on that Google Earth estimate of the Milky Way (wrong). I took some early photos to use as a foreground overlay. Then I realized that it would be many hours before the Milky Way would line up behind my scene based on how the stars began to appear. Live and learn. Here is a sample photo of that scene.

I had to recompose. The Milky Way was really to my left a bit. There were 2 typical street lights for general illumination of the park in that direction. The park outhouse was directly under the Milky Way, and a large grove of trees behind that. Well I can only work with what I have. I was not certain it was a good idea to drive to the lake boat dock because the shore was all trees. Boat docks rock and bob in the water, not a good tripod platform. Add to that I could hear coyotes in the area, I was not wandering far from the car. So I work with the outhouse.

The gear I was using was a Nikon D7000, Sigma 18-35mm Art lens, tripod with ball-head, L-bracket on camera, cable release remote. Camera was on Manual exposure, 20 second shutter speed, f1.8, ISO up to 2500. I just guessed with white balance, but did not really care since I would use the RAW files anyhow. In Portrait mode my remote shutter cable does not fit on camera, so I set the built-in intervalometer of the D7000 to take a photo every 30 seconds and let it go for around 8 minutes. I wanted a minimum of a dozen photos of the scene to stack, if not more. Then I dropped the ISO to 160, shortened the shutter speed to 13 seconds, and took some clean photos of the foreground to use as an overlay at the end of the workflow.

Sample image at ISO 2500, no workflow processing done.

Sample image at ISO 160, with some workflow adjustments done for the overlay.

I also composed another scene landscape mode aimed to the tree-tops.

That ends the field-work. I drove home, arrived at midnight, showered off the bug spray, and went to bed. The rest was done the next day.

I imported my images and actually began with using Sequator. It can work directly with RAW files, and is recommended to do this. You have the option of using TIF or JPG too. I imported my series at ISO 2500 and used the tool to define which part of the image is sky. It's easy to do, like using an erase tool in Photoshop. I set the processing to align both the stars and the foreground objects (done separately and recombined). I set some other options, experimented with how they worked. Since the stacking processing only takes a couple of minutes, it was not tedious to back-up and try different options. I then saved the output as a TIF and imported to GIMP as my preferred photo-editing tool. I adjusted white-balance, exposure, contrast, and boosted the saturation a bit. Then I took that ISO 160 image and pasted it over the star-stacked image. I added a layer mask to make the sky disappear in that layer, and blended it at the edges. I flattened the image down to 1 layer, added my watermark, and this is what we wound up with.

There is an option in Sequator to auto-remove artifacts like airplane and satellite streaks, but I either did not do it right or forgot to turn it on in this output. The best option is to remove the streaks with a photo editor, save as TIF, and import for stacking. I'm not feeling distressed by them.

There are numerous Youtube videos showing how to use Sequator and Starry Sky Stacker, so I won't dive into those details. The ISO noise smooths out by blending many layers together. The more layers to blend, the better the output. 1 or 2 dozen images would be recommended. The higher the ISO, the more layers that should be used. I did a manual overlay of the foreground image, but that was because the local lights were causing problems. If you have a nice exposure of the foreground with your star photos, the stacking may be all that is needed. Then clean up and adjust in your photo editor.

And here is the last composed scene I made, and not really the better one. I had to clone the foreground, darken it separately, and then overlay back on the image. The "halo" around the foreground is really there on the output of Sequator. I had the option on to reduce light pollution, but the horizon area where the pollution is worst, it appears to not work so good. Finding a dark sky with minimal light pollution is very desirable.

So there is an introduction to astrophotography. Easy, huh? Maybe next time out I will do intentional star-trails. Smile

BF Hammer - the new and improved screen name of Chris L

Edited 1 time(s). Last edit at 08/03/2018 07:55PM by BF Hammer.
Subject Author Views Posted
Photographing the Milky Way: How I did it. Jpeg Attachments BF Hammer 669 July 08, 2018 08:26PM
Just wow! (n/t) JohnSNY 396 July 09, 2018 12:43PM

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