Pictures of star trails are perhaps one of the most captivating images ever taken. Not just these star trails images are completely out of the world, they also give us an idea of how the Earth rotates in space. But have you ever wondered how they’re shot?
So, let’s see how to shoot and create astonishing star trails images.
1. DSLR – Point-and-shoot camera is an option, but a DSLR gives you much more flexibility in terms of shutter speed, aperture and ISO.
2. Tripod – A tripod is a must, because you would be required to overlap multiple images with the same composition. Unless you can create the same composition through multiple frames or manually stack photos in post processing applications like Photoshop, a tripod is required.
3. Remote Release – This can be avoided if you have a sturdy tripod that doesn’t move or creates image noise when you press the shutter button. Hanging a weight at center of the tripod might also prove helpful.
4. Stars – For general composing technique, you might want to include the Pole Star in the frame, but also you can do well without it.
Our aim is to capture a star trails image that shows the movement of stars while the Earth rotates. Since it is a slow process (360 degrees in 24 hours), you can’t capture that much rotation just by using long exposure. If you try to do that, you will end up overexposing everything but the stars; and the more the exposure you have, the more time your camera will take to write that file into the memory card.
I have a Nikon D5200, with which I took images with ~1 minute’s exposure and it took almost another minute to write those files into the memory card.
If you have ever captured astro photos before, then you’ll know that you can expose the photo only so much, until the stars’ movements become apparent. I once tried determining the threshold of exposure, just enough to get good light and not the trails and it turned out to be around 20 seconds (in Bangalore, India).
Anyway, as we’re specifically shooting star trails, it’s all right to get a bit of the movement, as we’re going to merge all images anyway. When I was shooting star trails, I set my tripod to compose the shot as I wanted, took some test shots to determine the right exposure, ISO and aperture, and started shooting the images.
Because my exposure was high (~1 minute) it took another minute to write complete JPEG and RAW files into the memory card, which made the time duration between consecutive shots to be 2 minutes. If you see the zoomed-in image below, you will see that there is an obvious gap between stars in the overlapped images. This is not good, but acceptable, because this image is really zoomed in. In the ideal case, stars in consecutive photos should overlap a little in order to create a perfect star trail.
Note: Depending on your camera, the time needed to write image files onto the memory card can significantly reduce. Higher range DSLRs have fast processors and hence low turnaround for disc write time. High speed memory cards also help.
While taking the shot, make sure to not displace your tripod. You must create images that overlap perfectly over each other. Otherwise, you will be spending way too much time stacking photos in Photoshop. Once set, the remote release must be tied to the tripod, because a hanging remote release may move the tripod a little bit and can mess up the composition. Alternatively, if your pocket permits, you can choose a wireless remote release option.
Now, it’s just a waiting game. Your remote release will take shots for you. The more shots you take, the longer the star trail you will get. I took 15 shots, out of which I discarded few that had too many clouds in it. It is totally up to the photographer to decide on how many shots he/she wants to take.
After you have taken the photos, the only thing left to do is to stack them. There are multiple softwares available to edit photos and some are specifically dedicated to creating star trail images. I personally use Adobe Photoshop and Adobe Lightroom. For this, I used Adobe Photoshop CS6 (any version will do).
To overlap images, open the first two images in Photoshop. Copy the second image and paste it onto the first one. This will create another layer on Photoshop. Now, right-click the new layer created and select ‘Blending Option.’ Now in Blending Options: Default, select the Blend Mode. You will see multiple options but don’t get confused. The blend mode you are looking for is Lighten. This will make sure that pixel values from both the images would be considered while merging the two layers.
You can play around with blend mode and opacity to see how you can get different effects on merging. Once you are done, select the blend mode: Lighten, and click OK. After that, right-click the new layer, and select merge visible. This will merge two layers into one by including both the images. Do this for all the images you have taken, and you will see star trails appearing.
Now apply any vibrant, contrast, etc. Your star trail image is ready.
Camera settings for a single image
Exposure: 50-60 seconds on an average
Focal Length: 25mm
Note: Same settings can be used to capture Milky Way photos as well.
Remember that the golden rule of photography applies to this as well – “Learn the rules, then break them”. Happy Shooting!
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