Photographing Star Trails

This article originally appeared on www.sigmaphoto.co.za

Hello from Udo Kieslich, I have prepared a short snippet on how to go about photographing star trails using Manual exposure mode, a Nikon D850 and a Sigma 14mm f1.8 Art lens. Shoot in RAW and use a Daylight White Balance setting.

With a digital camera, the best method is to take a sequence of 30 second exposures in quick succession and stack them together in Photoshop to create the light trails. This results in less noise and allows you to control the starting image for the trails, which determines the overall brightness of the sky. The more shots you take, the longer and denser the trails become – it is recommended you do at least 240 to 480 exposures, which translates to an exposure time of between 2 to 4 hours once the images are stacked together. The simplest is to use an intervalometer, which some cameras have built-in, or you can purchase a remote one. It is also best to have a battery grip with an additional battery connected to the camera, but if you don’t have one, make sure the in-camera battery is fully charged before you begin.

I prefer doing a separate exposure for the foreground, using the identical composition as I do for the sky. The two are then blended together in Photoshop. This allows you to use a smaller aperture (f11 or f16) to obtain a deeper Depth of Field. This allows for more flexibility when it comes to composition and also helps you obtain more detail, as you can take the foreground shot while there is still some ambient light around. For the foreground exposure it is important to turn the “Long Exposure Noise Reduction” feature to “On”, as it greatly helps reduce noise.

As a guideline for the foreground exposure I generally take this well after the sun has set, but before the ambient light has completely vanished. I set the camera to f11 and use the lowest native ISO, which is 64. Once the light meter indicates correct exposure using a shutter speed of 15”, I take my first shot for the foreground. Each time the ambient light diminishes by one f-stop I take another shot – in other words I’ll do a few more foreground exposures at 30”, 1 minute, 2 minutes and 4 minutes. During this time, the shaping and colour of light can change drastically, depending on the direction of the composition, in relation to where the Sun set. This allows for a few options to later blend with the star trails, to see which one works best for that specific image.

Keeping the composition exactly the same as you did for the foreground shot, make sure that the camera is accurately focussed on infinity or on the horizon and switch the lens to Manual focus, otherwise it will try to hunt for focus while photographing the stars. Set the camera to f4 | 30” | 400 ISO and on the intervalometer, set the number of shots you’d like to take in a row. A minimum of 240 shots is recommended, which would give you 2 hours’ worth of trails. Once the stars become visible and while there is still a bit of dark blue in the sky, start the intervalometer. Make sure to switch Long Exposure Noise Reduction to “Off” for the stars, otherwise you will end up with gaps in-between the star trails, while the camera reduces the noise.

I usually programme my camera to take at least 1000 shots in succession (which is pretty much an entire evening’s worth of star trails), as I then will always have the option on how long (and dense) I’d like the trails to be in the final image. Once you’ve downloaded the images, you’d open the star images in Photoshop ACR and apply the same edits to each image. You’d then stack them together in a layered file in Photoshop and select the “Lighten” blending mode to produce the trails. The foreground image would be edited to suit the overall mood of the scene, but the secret is not to make it too bright, otherwise it looks unnatural when you match the foreground with the sky.

This image was taken in the Richtersveld Tranfrontier Park, on the Orange River, which forms the border of South Africa and Namibia. The sky consists of 1040 thirty second exposures, resulting in an exposure time of over 8 hours, hence the very dense and long trails. I did a separate foreground exposure well after sunset, using a smaller aperture for a deeper depth of field. This helped get the rocks in sharp focus and the stacked sky was subsequently blended with the foreground using layers in Photoshop.

This is a vast topic that requires lots of practise and experience, but the hardest part is being scared of making a mistake and never getting going in the first place. There are many useful resources on the internet and we offer a Night Sky photography course at our college as well, but for now I recommend you download an essential night sky App called PhotoPills, and visit their website for further information on this wondrous discipline.

Udo Kieslich

Founder and owner of the College of Digital Photography in Johannesburg | www.codp.co.za.

Nikon D850 | Sigma 14mm f1.8 Art
Sky: f4 | 30″ | 400 ISO
Foreground: f11 | 120″ | 64 ISO