Back in September 2015, we were on holiday in Tenerife. If you weren’t aware, the island is essentially a large volcano, and the national park formed by the caldera is blessed with clear, dark skies.
I decided to try a panoramic shot of the milky way as I’d seen these done before, and a few people have asked how it was done. I’ll detail the process in this post.
Getting the source pictures.
The first step is getting the pictures. The summer milky way arches high overhead in the sky, reaching from the southern horizon to the north. This means you can’t fit it into one shot (unless you happen to have a 360 degree fisheye lens of course!), and we need to take several pictures to join together later.
As an aside, the summer milky way is when the brightest part (looking towards the centre of the galaxy) is visible in the northern hemisphere. The further south you can get the better which is another reason Tenerife was a great location. From the UK, the galaxy centre is much closer to the horizon).
The first thing you’ll need is a tripod. The exposures will be quite long and you won’t be able to handhold for over 20 seconds! Once the camera is mounted on the tripod, it’s time to work out the settings. Night sky shooting is tricky, because you need a long exposure to capture anything at all, but too long and the stars will trail, due to the rotation of the earth. First up, work out what the maximum exposure length you can use before the stars trail. The wider the angle of your lens, the longer you can shoot for (because any movement occupies a much smaller step on the final image). One quick way of working this out is called the “500 rule”. Simply divide 500 by the focal length of your lens. In my case, my lens is 16mm, so 500/16 = 31.25. The maximum length I can shoot without using “bulb” mode is 30 seconds, so that fits nicely. Pixel-peeping at 30s still showed a tiny bit of movement though, and I also wanted to shoot all my images in the shortest timescale to avoid stitching, so in the end I plumped for 25 seconds. It’s worth noting that a crop-sensor camera needs to reduce the time (as you’re effectively “zoomed in”, so divide the obtained result by your crop factor (i.e. for a 1.5 crop factor, 31.25 becomes around 20 seconds maximum recommended exposure time.)
Next up, decide on your aperture. This will generally be “as wide as you can go” to get as much light as possible. My wide angle zoom is limited to F/4, so if you’ve got an F2.8 lens or faster, you’ll be able to lower your ISO accordingly.
Finally, work out the ISO. If your camera has an auto ISO mode, then use that after dialling in the other two settings, and then set that value too (or just experiment!) It’s important to fix all settings to make stitching easier later on.
With your settings locked in, set manual focus and then focus to infinity (if you can zoom in and use live-view, all the better, otherwise take a test shot and adjust accordingly). Once focus is correct, take your pictures.
You’ll need to shoot a set of photos covering half the sky, from one end of the milky way to the other, and all the way down to the horizon on one side. Make sure there’s plenty of overlap between the pictures to aid stitching and avoid gaps later on. The more pictures the better! I took a screen-grab of Stellarium (planetarium software) to show the sort of minimum coverage you should aim for- the more the better as it’ll help later on, so if you have chance to cover a bit more of the sky and ground, do it.
OK, so you’ve got your pictures. Now what?
Step 1 is to import your pictures. I use Lightroom. Once imported, you have a bunch of thumbnails staring back at you:
The first step I took was to apply lens correction to the images. This removes any barrel distortion and vignetting from each image that’s inherent to the design of the lens, and is usually as simple as ticking a box in Lightroom. Don’t worry too much if you don’t have a lens profile however:
Next up, we want to stitch the images. There’s a variety of applications out there to stitch images, including an option in the latest versions of Lightroom CC- although it’s rather limited. I use the free Microsoft Image Composite tool, available here
It can’t read the RAW files direct from the camera, so you’ll first need to export them. When exporting from Lightroom, select 16-bit TIFF and don’t resize. 16-bit TIFFs preserve all the image data in the RAW files, whereas a JPG will throw lots of data away making the image difficult or impossible to enhance later on.
Once exported, fire up MS ICE, select “New Panorama from Images” at the top, and load all the TIFFs.
On Step 1, leave Camera Motion on “Auto detect” and click “Next”. It’ll now load all the images and attempt to align them. This could take quite a while so it’s a good chance to put the kettle on…
Once it completes, you’ll be presented with something similar to the below:
It looks a bit weird, but that’s ok. It looks strange as you’re mapping a sphere onto something flat- rather like trying to flatten an orange peel, and the same problem map-makers have had for years!
You can probably make out that the stars at the very top are flattened and stretched – that’s partly because I didn’t shoot my source images far enough out, but we can rescue it by clicking in the image and dragging around. You can move it up/down/left/right and rotate. After a few adjustments we have this:
Now, the arc of the milky way is more what we’re after, although with the downside of the ground being a little bent, but again, we can fix that later on. Once you’re happy, click Next. It’ll now go off and churn away for a while to create the panorama. You can auto-crop it on the next page (see below) but don’t do that, as we need the space around the image for some more adjustments to the geometry. It should look something like this:
Click Next. We can now save the image to disk. IMPORTANT- make sure you change the output type from JPG to TIFF, and tick the box to include the alpha channel, again to preserve the full colour and brightness information in the image for later enhancement!
Flatten the horizon
If you managed to get your nice milky way arc and a flat horizon within ICE, well done, you can skip this step! But if you need to make some final tweaks to the geometry, you’ll need to fire up Photoshop. You should now have a TIFF of your stitched image saved. In my case it’s a 211MB file, with dimensions of nearly 20000 pixels on the long side! Open it in Photoshop…
On the Edit menu, click “Free Transform”, then enable warp mode with the little grid button on the toolbar:
You can now move the two bottom warp-points upwards. This will let you flatten out the ground horizon without distorting the stars above. I moved mine this much (adjustment points circled in red):
Finally, you can crop the image to remove the extra parts before saving:
When saving, again make sure you save as a 16-bit file to preserve details.
Making it look pretty
So we now have our stitched image, but it’s a bit dark. The fun part is bringing out all the details, and for this I use Lightroom. There’s no right or wrong here, as it’s open to artistic license. You can try and go for a realistic result, or something a bit more dramatic… up to you. To start with, we need to brighten it so we can see something!
To begin with, lets do some basic edits:
That’s looking a bit better, but the stars are strangely blue… I upped the white balance temperature to warm up the image a little (+10 to begin with) which helps, but zooming in to 100%, the stars often have a slight blue halo around them – not uncommon with lenses when they’re wide open, and stopping down to F5.6 would have reduced it. In this case though, I can just lower the blue saturation slider (and increase it’s luminance) in Lightroom. Things look a little better now:
That’s looking ok, and reasonably realistic (I guess) but I wanted a bit more impact. I turned up the saturation by 75 or so, and added a little more contrast. Next, I opened the image up in Color Efex Pro 4, part of the Nik Collection (now sold by Google). I added a Cross-Processing filter at a low level, and used the Pro Contrast filter too. After those adjustments we’re back in Lightroom with the below (I also tightened the crop a little)
Finally, I want to add a bit more definition to the dust clouds before applying a final noise reduction. To do that, we can use the adjustment brush in Lightroom. Set the brush to have a soft edge, and paint over the dust clouds (highlighted in red):
By increasing the contrast/clarity and a couple of other alterations, we can bring out a bit more detail in the milky ways structure:
The final few tweaks were:
We now have the image is below:
It’s not perfect- there’s a couple of dark lines in the middle of the picture. I think these are where I didn’t overlap the source images quite enough. They can be reduced with another adjustment brush, increasing brightness and reducing contrast/saturation a little. You’d need to use a bit of trial and error, but they’re less noticeable.
That’s about it, here’s the final image:
To summarise, the basic workflow of something like this is: