How To Shoot Star Trails

Images of star trails are perhaps a few of the most captivating images ever taken. But have you ever wondered how they’re shot? Even though these star trails look completely out of the world, they give us an idea of how Earth rotates in space and why the pole star is known as the pole star. So, let’s see how to create star trail images.

Equipment required

1. DSLR – Point-and-shoot cameras may also work here, but a DSLR gives you much more freedom in terms of shutter speed, aperture and ISO.

2. Tripod – A tripod is a must, because you would be required to overlap multiple images. Unless you can create the same composition through multiple frames or manually stack photos in Photoshop, a tripod is required.

3. Remote Release – This can be avoided (only to an extent) if you have a sturdy tripod that doesn’t move when you press the shutter button. Hanging a weight at centre of the tripod might prove helpful. I would suggest you try your hand at capturing star trails once. Only after that will you realise its importance and all the problems you might face if you don’t have a steady camera. Try practising before going on a star trail shoot for a whole night. It will give you an idea of exactly what its like, before going to the mountains and trying it out.

4. Stars – For general composing technique, you might want to include the pole star in the frame, but many great photographers have done amazingly well without it. The same rule applies to this as well – first learn the rules, then break them.

Technique

So, our aim is to get a star trail that shows the movement of stars while the Earth rotates. Since it is a very slow process, (360 degrees in 24 hours), you can’t capture that much rotation just by long exposure. If you try to do that, you will end up over exposing 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 D3100, with which I took images with ~1 minute’s exposure and it took almost another minute to write those files into the memory card (even with speed x10 memory cards). Hence, you have to take care of that as well.

If you have ever clicked 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 17 seconds (in New Delhi, India), but that is a topic for some other discussion.

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 overlapped image. 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 so as 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 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, which can be really annoying. If there is wind, you can hang weight at the centre of your tripod; it really helps. Once set, the remote release has to be tied to the tripod, because a hanging remote release may move the tripod a little bit and can mess up the composition.

Now, it is all 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 10 shots, out of which I discarded one 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.

Post-processing

The following four photographs may look the same, but these are different photographs that will eventually be merged to make a star trail image.

There are multiple softwares available to edit photos and some are even specifically dedicated to creating star trails.

I personally use Adobe Photoshop CS6 and Adobe Lightroom 5. For this, I used Adobe Photoshop CS6.

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 they help you get different effects on merging. When 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 vibrance, contrast, etc. Your star trail image is ready.

EXIF data for a single image

• Exposure: 55 seconds on an average
• Aperture: f/10
• Focal Length: 28mm
• ISO: 400

Happy shooting!

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