Creating star trails can be an exciting and rewarding experience for landscape photographers. It involves capturing the movement of stars across the night sky over an extended period of time. In this comprehensive tutorial, I'll guide you through the entire process of creating stunning star trails, from planning and shooting to post-processing.

Equipment Needed:

Camera: Any modern DSLR or mirrorless camera with manual mode and long exposure capabilities will work.
Wide-angle lens: A lens with a wide field of view, ideally between 14mm to 24mm, will capture more of the night sky.
Sturdy Tripod: A stable tripod is essential to keep your camera steady during long exposures.
Intervalometer: If your camera doesn't have built-in interval shooting, an intervalometer will be needed to automate the process. I’d recommend any that connect via wifi or Bluetooth rather than cable as you want to minimise touching your camera during long exposure shots as much as possible.

Planning the Shoot:

Location: Choose a location away from light pollution to minimize unwanted ambient light and enhance the visibility of stars. Look for interesting foreground elements like rocks, trees, or water to add depth to your composition.
Time: Pick a night with a new moon or when the moon is not visible to avoid its bright light interfering with the stars.
Weather: Check the weather forecast for clear skies. Avoid shooting on nights with heavy cloud cover, as it will obstruct star visibility. If you’re shooting near the beach it may also be prudent to check tides and swell data to ensure you won’t be washed away from your spot.
Mobile phone: Use apps like PhotoPills (night AR mode is super useful here), or Star Walk as well as your compass app on your phone to help you position your camera for the composition you have in mind. In the southern hemisphere you need to be facing south to get nice circular star trails and in the northern hemisphere you need to face north.

*The right foreground can add interest to your final image*

Camera Settings:

Shoot in RAW: RAW files retain more information and allow for better post-processing.
Manual Mode: Set your camera to manual mode to have full control over the settings.
Aperture: Use a wide aperture (e.g., f/2.8 or f/4) to gather more light and capture faint stars.
ISO: Start with an ISO between 800 and 3200, depending on your camera's capabilities and the darkness of the sky. Lower ISOs will allow for more colour from the nebulas to appear in your final star trail. Higher ISOs may introduce more noise, so find a balance that works for your equipment.
Focus: Switch to manual focus and set it to infinity. Perform test shots and adjust until the stars appear sharp and clear.
Image Stabilization: If your lens has image stabilization, turn it off when shooting on a tripod to prevent interference.

Shooting Star Trails:

Compose your Shot: Frame your shot, considering the foreground elements and the desired composition.
Bulb Mode: Use the Bulb mode or a manual exposure setting to control the exposure time beyond the camera's standard shutter speed limits.
Intervalometer: Connect your intervalometer or use the camera's built-in interval shooting feature to automate the process and reduce camera shake during long exposures.
Exposure Time: Start with an exposure time between 15 to 30 seconds per shot. Longer exposures may lead to overexposed stars, especially if you are in a light-polluted area.
Continuous Shooting: Set the intervalometer to take a series of continuous shots with the same exposure time until you have enough frames to create the desired star trail effect. The number of shots required will depend on the length and intensity of the trails you wish to capture. Aim for at least 100 images. The more images you take, the longer your trails and the smoother your final ‘disc’. See below for the difference between half an hour worth of shots and 2 hours worth of shots.
Avoid Gaps: To avoid gaps in the trails, keep the interval between shots short (1-2 seconds) or use the "Exposure Time + Interval" method in your intervalometer settings.

*Half an hour worth of images. Stars will move a fair distance in that time over the night sky!*

*2 hours worth of trails. The ‘disc’ formed is smoother and more complete with more images*

Post-Processing Star Trails:

Import Images: Transfer your RAW images to your computer and import them into photo editing software. Adobe Bridge or Lightroom, or similar programs work well.
Select Key Frames: Review your images and select the best few frames to serve as the base for your star trails. Choose images with minimal noise and sharp stars. I do some basic edits now in Adobe Camera RAW (see my tutorials on star stacking for my workflow) and save my files ready to import in to Sequator.
Stacking Software: Use star trail stacking software like Sequator, or Adobe Photoshop (with "Statistics" or "Lighten" blend mode) to merge the selected frames into a single composite image.
Noise Reduction: Apply noise reduction techniques to the stacked image to minimize noise and improve overall image quality.
Adjustments: Make adjustments to contrast, brightness, and color balance to enhance the visibility of the star trails and foreground elements and bring out the colours present in the star trails. Be cautious not to over-process the image.
Finishing Touches: If desired, apply additional post-processing techniques such as dodging and burning to emphasize certain areas or removing unwanted elements using the clone/heal tool.

Tips and Tricks:

Bring extra camera batteries, as long exposures can quickly drain power.
Cover the viewfinder with a cloth or a viewfinder cover to prevent light leaks during long exposures.
Consider using the "Dark Frame Subtraction" technique to reduce hot pixels and sensor noise during long exposures (see below).
Experiment with different compositions, foreground elements, and light painting to create unique and captivating star trail images.

Dark Frame Substraction

Dark frame subtraction is a technique used in astrophotography to reduce the appearance of hot pixels and sensor noise in long-exposure images. Hot pixels are bright, colored dots that can appear in photographs, especially in longer exposures, due to the heat generated by the camera's sensor during operation. Dark frame subtraction is an effective method to minimize these unwanted artifacts.

Here's how dark frame subtraction works:

Capture a Dark Frame: To create a dark frame, cover your camera's lens and take a photograph with the same settings (ISO, aperture, and exposure time) as your star trail images. This dark frame should be captured immediately after your star trail session without moving the camera or changing any settings. The idea is to record only the heat-generated noise without any light from the stars or the environment and so you want your camera sensor to be at the same temperature (not not have warmed up in your camera bag / car).
Identify Hot Pixels: The dark frame contains information about the hot pixels and sensor noise that are specific to your camera's sensor. These hot pixels appear as bright dots against a dark background in the dark frame.
Subtraction Process: In post-processing, open both the dark frame and the stacked star trail image in an image editing software that supports dark frame subtraction (eg/ Sequator). Most dedicated astrophotography software and some photo editing tools have this capability.
Align Images: Make sure the dark frame and the star trail image are perfectly aligned. You can use image alignment tools or manually adjust the positioning to ensure a precise match.
Subtract the Dark Frame: Use the "subtract" or "difference" blend mode to apply the dark frame over the star trail image. This process subtracts the hot pixels and sensor noise present in the dark frame from the corresponding areas in the star trail image.
Result: The final result is an image with reduced hot pixels and noise, giving you a cleaner and smoother star trail photograph.

Keep in mind that dark frame subtraction works best when the camera's sensor temperature during the dark frame capture is similar to the temperature during the star trail session. If you shoot star trails in cold conditions and the dark frame is captured in warmer conditions (or vice versa), the effectiveness of dark frame subtraction will be reduced.

By incorporating dark frame subtraction into your astrophotography workflow, you can significantly improve the quality of your long-exposure star trail images and achieve more stunning results.

Remember, practice makes perfect! The more you experiment with star trail photography, the better you'll become at capturing breathtaking night sky scenes. Happy shooting!