In this video tutorial I walk through a technique for reducing noise and improving image quality by combining multiple astrophotography exposures. I also demonstrate what to do when auto-alignment tools, like Photoshop’s Auto-Align Layers function, fail to properly align your images.
Lately, I’ve been on an exposure stacking kick. Combining a bunch of consecutive exposures of the night sky can greatly improve image quality and it has allowed me to use smaller, cheaper and more compact gear (like a point and shoot or even a smartphone) without making too many compromises in image quality. Stacking is a technique that’s been used by astronomers and astrophotographers for decades. Most of the telescope photographs that you see from observatories like the Hubble Space Telescope were made by combining hundreds of separate photographs with hours and hours of data to yield such beautiful images of the night sky.
In the video tutorial below, I walk through the techniques that I use to combine several exposures of the Milky Way using Adobe Photoshop. The resulting photograph from combining just 8 separate exposures offers a great improvement in the quality of the image by reducing noise and revealing more detail.
If you’re drooling over the latest, expensive camera body and lens offerings in hopes to improve your landscape astrophotography, consider using image stacking instead of spending a boatload of money on new equipment. You’ll find that with some careful use of stacking, even a basic DSLR with manual controls can make some very high quality images of the night sky.
What to Expect (Before and After)
Sony RX100III, 8.8mm, f/2.8, ISO 1600, 8 x 20 seconds
In the video tutorial below, I use some relatively noisy sample images made with the Sony RX100III (read our full astrophotography review). You can see the before and after example image above. This particular tutorial focuses on the use of the Adobe Lightroom and Adobe Photoshop and addresses one of the common problems that many of our readers have experienced when following my original video tutorial on Landscape Astrophotography Image Stacking when using these pieces of software.
Stacking un-tracked exposures of the night sky requires alignment of each exposure to compensate for the rotation of the Earth. Photoshop has an auto-alignment tool that can line-up multiple exposure layers but sometimes the tool will fail to properly align the images, resulting in a low-quality final image with blurry stars. There are a lot of reasons that Photoshop might fail to align your layers: clouds, lens distortion, and even light pollution can prevent automatic alignment.
This video walks through the method that I use to align my exposures after some basic edits and I also cover what to do when the auto-align layers feature in photoshop fails to work properly. Check it out and let me know what you think in the comments.
Photoshop Exposure Stacking Video Tutorial
Alternative Layer Auto Alignment and Star Stacking Software
Adobe Photoshop is typically my primary go-to piece of software for stacking landscape astrophotos but I should also mention some of the other options that you may want to try that may produce good results. Even if it is my personal choice, Photoshop can be a beast of a program and it’s not purpose built for astrophotography. Most of the below pieces of software are made for photographs of deep sky objects but they can often also be used to make stacks of wide angle landscape astrophotos too.
I’ve had varying results on each of these pieces of software. Sometimes they work perfectly and other times they too will have problems with alignment but they’re worth a shot if you’re looking for other automatic options. If you know of any other software tools that you think other photographers will like to try, let me know and I’ll add them to this list.
Starry Landscape Stacker is probably the most intriguing of all the software packages that I’ve used. It’s only available for MacOSX but it automatically stacks and masks landscape astrophotography, perfect for the stuff that we love to make at Lonely Speck. I’ve had generally good success with small stacks (8-12 exposure max) but it starts to produce mixed results if too many exposures are used. I’m still putting the software through the paces but I plan to make a quick video walkthrough of Starry Landscape Stacker in the near future. If you’re on MacOSX, this is a great App to try.
DSS is probably the most well-known astrophotography stacking program. A lot of Lonely Speck readers have shown me their excellent results from the use of DSS. It’s completely free and available for use on Windows.
Nebulosity is an image stacking program that’s available for both Mac OSX and Windows. I’ve had the most success with Nebulosity when using longer lenses (50mm and longer) and mixed results with untracked stacks using ultra wide angle lenses. You can download and try it in demo mode to see if it works well for you.
In order to give you a better idea of the results that we can expect from image stacking, check out these before/after examples of image stacks made with the technique outlined in this tutorial.
Sony RX100III, 25.7mm, f/2.8, ISO 1600, 8 x 10 seconds
Sony a7II, 55mm, f/2.5, ISO 1600, 32 x 5 seconds
Sony RX100III, 8.8mm, f/2, ISO 1600, 54 x 20 seconds
Sony a7II, 50mm, f/2.8, ISO 6400, 16 x 6 seconds
Try out exposure stacking! While you’re out shooting the Milky Way, take a few extra exposures and try combining them in post processing. Even just a few exposures combined in post processing can make a huge difference in final image quality. Stacking can greatly improve the results you can get from very limited equipment. I have made it a normal practice in almost all of my astrophotos and I’ve seen a great boost in image quality as a result.
I hope this tutorial was helpful, let me know if you have any questions in the comments section below.
- Sony RX100III (Amazon / B&H)
- Sony a7II ( Amazon / B&H )
- Sony 55mm/1.8 (Amazon / B&H)
- Sirui T-025X Compact Carbon Fiber Tripod ( Amazon / B&H )
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