Nightscape astrophotography combines the beauty of the night sky with gorgeous landscapes after dark. While some compositions can take hours to capture, with multiple tracked shots of the sky and multiple foreground images, you can simplify the process by using a single long-exposure image.
Incorporating both the sky and Earth, a single image can display the environment and showcase the raw beauty of the night, transporting those who look at it closer to a real-life experience. Single long-exposure (SLE) images are, in a sense, a projection of an astrophotographer’s experience in the field. Read on to explore the technical as well as the philosophical side of single long-exposure images.
Nightscape techniques
Nightscape astrophotography, or astro-landscape photography, can broadly be divided into four categories based on the techniques used to capture it:
1. Untracked and single: You capture a single image showing the night sky and the landscape.
2. Untracked and stacked: You place your camera on a tripod and take multiple images. These images are then stacked to improve the signal-to-noise ratio.
3. Tracked and single: You take a single tracked image of the sky and an untracked image of the foreground to blend them together for the final result.
4. Tracked and stacked: You track the night sky with a star tracker and capture multiple images. This also requires a different set of foreground images (single or multiple), which are blended during processing.
There are also panorama images that capture multiple sections of the sky using any of the above-mentioned techniques. This article will mainly discuss the first option, “untracked and single.” But we’ll also see how “tracked and single” can be captured, with a twist.
Single images go a long way
An SLE is not meant to capture the intricacy of the night sky. If you’re looking to get the best details of the Milky Way’s arms or a large nebula, track and stack your image. An SLE is meant to capture the environment. These images are what I call composition-heavy. While composition is important to all nightscape images, SLEs rely mostly on the overall shot, rather than its intricate details.
A photo of an automobile with the Milky Way or a historical monument with a constellation should tell a story — a story of Earth and sky at night. If you are looking to document the region, the night sky, or simply want to convey how dark your night was, go with an SLE. And the best thing about this technique is that it’s beginner-friendly.
Plan and photograph: One click
Like any other nightscape images, SLE images need to be planned. That planning can either begin at home, with the help of apps like Photopills, Google Earth, etc., or by reaching the field early. Scouting the field in daylight (or even twilight) will give you an idea of your surroundings, which can be difficult to gauge at night. However, one advantage of SLE images is that you don’t have to plan ahead. Just by looking at and feeling your surroundings, you can decide to set up your camera and tripod and take an image.
While photographing the Milky Way, constellations, or asterisms with your camera on a tripod, if you don’t want star trails in your shot, you are bound by the Rule of 500: The maximum allowed shutter speed should be 500 divided by your lens’ effective focal length. For example, if you’re using a 20mm lens on a full-frame camera, your maximum shutter speed would be 500/20 = 25 seconds. (If that same 20mm lens is on a crop-sensor camera, the effective focal length will longer by a factor of about 1.5, yielding a maximum shutter speed of 500/30 = 17 seconds.)
However, in order to get sharper stars, I would recommend using a different rule: the NPF rule. Here, N stands for the f-number (or f/ratio) of your lens (f/2.8, f/4, etc.). P represents the pixel density, or how tightly the pixels are packed on your sensor. To find this number, divide the width of the sensor by the number of pixels along the width. Finally, F is the focal length of your lens. These values should all be in the same units (typically millimeters). The NPF formula is: maximum exposure (in seconds) = [(35 x N) + (30 x P)]/F. Choose an f/ratio (N), calculate your maximum exposure time before stars begin to trail, and choose your ISO. Try out different ISOs to see what level of noise is acceptable.
For SLE images, you can also use a star tracker at the ½x sidereal rate. This will allow you to get a longer shutter speed (compared to the previous method of untracked), giving you a much cleaner image. However, the maximum shutter speed will now depend on the distance of your camera from the foreground subject. The farther the foreground object, the longer the shutter speed you can use.
If you are close to your foreground subject, tracking the image will blur it, even with a short shutter speed. You’re better off shooting untracked in such cases. The tricky part for these images is that there are no rules to calculate the optimum shutter speed. I have tried exposing for 60 seconds with a 15mm lens and 20 seconds with a 50mm lens with no noticeable blur in the foreground. In both cases, the foreground subject was distant. Experiment with different shutter speeds to find the sweet spot, and be sure to note it for future reference.
If you’re doing a star, planet, or Moon trail, there are no limits to your maximum exposure length. You can shoot for a few minutes or a few hours. But how do you pick the right settings? It’s simple. Take a short test shot of four or five seconds with a high ISO through the lens’ largest aperture. Tweak the ISO until you get the desired histogram curve. Now, adjust your shutter speed to the desired exposure, counting how many additional stops of light you are adding. (Each doubling of exposure length is an additional stop.) For each stop of exposure length you add, compensate by reducing ISO by one stop (a factor of two) or stopping down your aperture. Or, to make things really easy, put your current exposure details into an app like Exposure Calculator and adjust the aperture and ISO within the app until you get the desired exposure length.
Compose strong, but simple
Remember what you’re trying to show: the serene night sky and the place you are at. Your surroundings are as important as the starry night sky. Look around for the most interesting subject in the field. As a tool for storytelling and documentation, SLE images require a meaningful composition. Your foreground subject could be anything — a tree, a rock, a car, whatever.
As far as the sky is concerned, start with a something big. Look for the Milky Way or large constellations like Scorpius, Ursa Major, or Orion. Smaller targets like a rising or setting Moon or even bright planets like Venus or Jupiter will also do the trick. While sharp stars convey a sense of calm, trailed stars convey a sense of movement. It’s up to you how you’d like to portray your story.
Processing
The last step in creating a mesmerizing SLE shot is processing. These images can be processed like others with Lightroom, Camera Raw, Photoshop, or any similar software. However, to bring out the best in SLEs, photographers employ a technique commonly used in landscape photography, known as “double-processing” or “dual-processing.” As the name suggests, the image is processed twice. The first time focuses on the foreground. Then the RAW image is again processed, focusing on the sky. These two versions are then blended together using a mask.
Always remember, to convey the true environment, the processing should be rather minimal. While this is not a rigid rule, minimal processing helps keep the image true, a key criterion for documentation and storytelling. Because you’re taking a single exposure, there might be visible noise in your image. Modern cameras, however, are capable of handling extremely high ISOs and still producing a presentable image. Your processing can include careful noise reduction, but make sure your image doesn’t get too soft. Remember, noise is not going to ruin your story. A little bit of it is no problem.
Dual processing
Dual processing involves processing the same image twice, each time focusing on different aspects (e.g., the sky and then the foreground) and blending the two versions for the final image. This shows the night sky from the banks of Pangong Lake in India.
SPECS: Nikon Z 6II camera; Nikon Z 20mm lens; 900-second exposure; f/4; ISO 800.
Credit: Soumyadeep Mukherjee
Nightscape imaging simplified
As amateur astronomers strive for more complex forms of nightscape imaging, with increasing difficulty and time, usage of multiple filters, and advanced processing techniques, SLE images sit quietly as an act of simplicity. The process of taking images becomes just you and the world under the stars. They capture the night as it unfolds in front of you, a story embedded in time. A simple click of your camera transforms into a document you can revisit years later. It is an image that nobody can reproduce, even from the same location. SLE images show the unique nature of the night sky, the coolness of the winds and the warmth of the stars. And, as an uncomplicated form of nightscape photography, even beginners can enjoy success.
Your only worry in shooting long single exposures is the possibility that satellite trails will mess up your images. One approach to mitigate this is to shoot late at night, when Earth’s shadow has covered much of the sky and sunlight doesn’t reflect off satellites overhead.
In a way, single images are a tool for honest storytelling and documentation, standing far from composites. A simple composition, one click of the camera, and minimal processing is all you need. Because sometimes, less is more.
Soumyadeep Mukherjee is an amateur astrophotographer, astrophotography educator, and writer from Kolkata, India.
