We are about to head into the next stargazing season down here in the Southern Hemisphere – I thought this would be a good opportunity to talk about something that many astrophotographers like to do but can seem quite complex – making a panorama of the Milky Way. In this tutorial I’ll go through a couple of my recent panoramas and explain the process used to capture the frames and the software I used to create the final pano. If you haven’t done any astrophotography before then make sure you take a look at this awesome tutorial from Lonely Speck before starting.
The software I’ll be using to make my panoramas is PTGui – it’s not free, but suits what I do – it can also stitch RAW files, which works for me. If you want to try a free option, consider MS ICE – a very powerful tool that works most of the time as well as being quite user friendly. Another option is Hugin, which is immensely powerful, but a little hard to get your head around first time. I honestly haven’t had much success with Lightroom or Photoshop’s panorama stitchers, but you might have more luck! I generally start with PTGui, then move to MS ICE or Hugin if for some reason PTGui isn’t happy – but this is rare.
Why Even Do a Milky Way Panorama?
First up, why would you want to? There are a number of reasons – firstly, and most commonly, a panorama gives you the opportunity to create a composition that isn’t always possible with a single frame. Composition is a huge part of photography so getting the right feel to your final image may necessitate a pano.
Secondly, you might want to take a panorama to take advantage of a fast lens, which will allow more light to hit your sensor, getting brighter pictures. For example, I have a Samyang 14mm f/2.8 lens – a really nice fast lens. However, I also like the sharpness of my Sony 55mm f/1.8 lens, but this obviously doesn’t capture as much of the landscape, so I need to do a panorama to get the same composition. Also, check out this tutorial on how different focal lengths affect your final astro shot.
Third, doing a panorama with a longer focal length gives you far more detail in each frame, meaning your final panorama will not only be far bigger (pixel-wise) but also allow you to reduce the size of the panorama, reducing the noise. When trying to capture a large sky with a single frame the noise from taking the shot will need to be reduced in post-production or with layering multiple images (something I’ve not mastered, I must admit!). However, if you take a panorama you can then reduce the overall size of the final image, significantly reducing the noise in the image. To give you an idea of the improvement in detail here is a 100% crop of Antares (the bright yellow star in the centre of Scorpius) with a Sigma 24mm f/1.4 lens and the Sony Sonnar t* 55mm f/1.8 CZ lens.
Two Panorama Styles
There are far more than two types of night time panorama, but I’ll talk about the two most common. The first is where the Milky Way appears flat and rises straight into the sky. The second is where the MW arcs across the sky in a semi-circle. Let me start by saying that BOTH are real. BOTH are taken in the same manner – the only difference is that the arcing panoramas are shot with a much wider view of the sky. What the photographer is doing is capturing the MW all around them and the final stitching software tries to make sense of the images by keeping the land flat (as it should be!) and the stars arcing in a semi-circle. If we had eyes that had a field of view that wide it would be how we see the stars, but we don’t, so we are more used to the ‘straight’ MW style.
So, here are two styles I’ve taken recently. First, the arcing version across Mt Sunday, Canterbury and the second, the more straight MW shot rising out of the Pacific Ocean. Both of these are after I’ve processed them. I’m not going to cover processing here, but if you want to have a go at processing night shots, take a look at my tutorial here (with a downloadable RAW file).
Taking panoramas at night is NOT easy. During the day you have plenty to see and can easily make sure you overlap each frame. At night, it’s much harder to see the landscape in the foreground and, after a while, all the stars look the same through a tiny LCD lens. Can I recommend you get an indexing tripod that will automatically lock to the pan/pitch you need for each frame or, if you’re cheap like me, use a tripod head that has some etchings (or stickers) that let you know how much you should pan/pitch. I use a birdswing tripod head (can’t afford much else right now) and I printed off some degree marks and stuck them on. I know exactly how much I should pan/pitch for the lens I’m using and I keep to that when out at night. Here’s an example of what I have (taken on a hike in the Port Hills when I lugged my huge tripod up and forgot the quick release plate – genius!).
Taking the Individual Frames
Ok, let’s get started with how you take the frames. This gets harder the longer your focal length. I strongly suggest you practice with a nice wide lens to start with. What I generally try to do is capture a panorama as normal but allow for a far greater overlap between frames (at least 33% overlap). So, in the image below, I took the bottom right shot first, then the bottom middle shot, then bottom left. I then raised the pitch of the tripod to take the 4th image and panned right – this technique is called a serpentine mosaic panorama as it snakes backwards and forwards up the image – it works for me because I can focus on just overlapping with the last image I’ve taken, rather than trying to remember where the first image was and pitch upwards from there.
One thing to remember is that the earth is rotating ALL the time. So, even if you’re only out taking photos for 10-15 minutes the whole frame will move. This is why I always start at the bottom and go horizontally first. If you go vertically by the time you get back to the bottom for the next row of frames the earth has rotated and the stars you want to capture have fallen behind the horizon. Definitely shoot horizontally to avoid this. As I said, with a longer lens, this is a really risky technique – one dud frame and the other 14 are wasted – check each frame quickly after shooting to check there hasn’t been any shaking or blur that you don’t anticipate before moving the tripod to take the next frame.
With the arcing style of panorama you need to capture a far greater field of view so I strongly recommend you do this with a wide lens. Again, start at the bottom and pan your tripod across the horizon first, then pitch upwards and take frames of the sky. The Milky Way will dip into the horizon at two points of the sky – I generally start at one end of the Milky Way and pan all the way to the other size of the horizon where the Milky Way has intersected the horizon. I might even get a few frames past where the MW stars and stops to give me more data, just in case I want to crop the image later. You can see I took the ground images first, then went back and got some other extra images of the edges, just to be sure. I was freezing cold by this time, so don’t blame me for not getting it right first time!
Stitching your Panorama
As I mentioned earlier I’m using PTGui for my stitching. I export the frames I want to stitch as DNG files and then load them into PTGui and click ‘Align Images’. 8 times out of 10, this is all I need to do and the image stitches beautifully.
However, occasionally, the software doesn’t work nicely. This happens where there isn’t enough information in the frames for the software to make a match between individual frames. This happens a lot more with Astro images because it’s hard to identify stars/foreground etc, as everything is so dark. PTGui and Hugin both allow you to add in ‘Control Points’ – these are when you manually add links between two different frames. So, if there’s a star that looks the same in both frame 1 and frame 2, you can manually tell the software that they’re the same thing and it’ll try to keep linking the images with your control points as a headstart. This can be a tedious job, but it’ll mean you get a panorama out of your frames rather than throwing it all away. As you can see below, the software didn’t see any overlap between frames 4 & 5, even though we can clearly see there’s heaps of overlap. It’s most likely because the frames aren’t level with each other and there’s a lot of distortion with the lens I’m using, so the software gets confused. Also, the lack of light in the images makes it really hard to spot the ‘right’ things to link – after a while, all mountains and stars look the same to the software!
Now, I’ve manually added in 9 control points. You want to have at least 4 control points per linked frame – the more, the better! PTGui gives you a nice magnifying glass to isolate the linked area to make sure you are linking the right things in each frame. Once I’ve added in enough control points I try to have the software fill in the gaps and re-align the images. Usually, this is enough to get a nice panorama. If by this point it still isn’t working then I generally get frustrated and walk away and try again another night – but you can keep adding manual control points until you get it right.
Choosing your Panorama Projection
Once you have enough control points PTGui will spit out a draft ‘projection’ or view of the panorama. This is where you can really play with your panorama to get the feel you like. PTGui will give you what it thinks is the best look based on the data is has, but I always like to choose different projections and use the one I like the look of. You can also move the image around and rotate it to suit your composition. It takes some practice, but play around – I’m sure there are cartographers out there that can help explain what the different projections mean, but I just try them out and go with the one that looks good. Here are 3 different projections – I finally chose the Mercator projection for this image.
PTGui allows you to use a masking tool to adapt the stitching. This comes in useful when you want to specifically include or exclude a certain frame. In the example below I spotted a satellite I liked the look of – I’d like to have it in my final image, so I’ve used the ‘Green Paint’ tool to force the software to include it in the final panorama. I could equally use the ‘Red Paint’ tool to force data out. I did this to exclude the beach in this image – it was quite close to the edge of the frame, so was a little noisier and more distorted than other frames – so, let’s make sure it’s not used in the final stitch. Again, pretty simple stuff – make sure you experiment to see what suits you 🙂
Exporting for Post-Processing
The final step is to export your panorama for any post-processing you want to do. I generally export in a Photoshop format so I can edit it in PS with Nix (my preferred editing tools). Tiff is also a good export format. Don’t edit astro shots with jpg – it’s just not powerful enough for the detailing you want to do. I usually just export the blended image BUT, you can also export the individual layers if you spot something later you want to edit back into the image that PTGui has removed – remember, the more layers, the bigger the file. This file was nearly 2GBs big with just the blended panorama.
Time for you to have a go…
And that’s it! Time to post-process, which is up to you. To help you practice, I’m including 6 smaller tiff files of my image ‘straight’ pano image. Use them, abuse them under Creative Commons BY-NC (you can do whatever you want with them, even manipulate the images, just don’t use it for commercial purposes and credit Ekant Veer and www.EkantTakePhotos.com as the source of the images). The images are SOOC (no editing) so you get to play with the entire process. If you want to do some lens correction and the info isn’t in the EXIF the images were taken on a Sony A7ii with a Sony Sonnar t* 55m f/1.8 lens.
If you have any questions, let me know and I’ll do my best to help out!