photographing star trails

see also:

• astrophotography
• astrophotographic landscapes of the Milky Way

• star trails are the apparent motion of stars in the sky due top the rotation of the earth
• the stars rotate around the south celestial and north celestial poles at a rate of approx. 360deg per day = 15 deg per hour
• the further from the poles, the longer the trail will be for a given time period

Sony a7RIV with Sony 14mm f/1.8 lens at ISO 800, f/2.2, WB 4000K, 35 minutes of 30sec images developed then stacked as jpgs using Lighten blend with VMax setting in Affinity Photo software South Celestial Pole taken from South Bruny Island, Tasmania latitude 43degSth with very low light pollution levels The two fuzzy bluish areas to right of the pole are Magellanic Clouds

• select a dark sky location away from light pollution
• consider having something of interest in the foreground (you may wish to take an initial single shot of the foreground using different exposure settings)
• use a camera with a wide angle lens on a tripod manually focussed on the stars
• ensure battery is fully charged
• depending on your level of light pollution, set your camera exposure to something like RAW file mode, manual exposure, ISO 800, f/2.2, WB 4000K, 30secs (60secs if your camera has this) - do a test exposure and adjust as needed - if your lens only opens to f/4 as its widest aperture then you may need to use ISO 1600-3200
• turn off long exposure noise reduction (as this will take another 30sec “dark frame” or blank photo resulting in gaps in your star trails)
• turn of image stabilisation (“SteadyShot” on Sony)
• after you have done some test shots and happy with focus, composition and exposure, set the camera to intervalometer mode:
  • on Sony:
    • it is called Interval Shooting Func which Shoot Mode/Drive 1 page of Camera 1 menu
    • set Interval Shooting = ON
    • Shooting Start Time = 1 sec (ensure there are no visible gaps in trails)
    • Shooting interval = exposure duration + 1sec eg. 31sec if shutter set to 30secs
    • Number of shots = 2x total exposure duration = as a minimum this probably should be around 60 for 30 minutes long trails but you could do much longer
• now you are you are ready to start shooting press the shutter button and leave it

• use your favourite photo editor to adjust the contrast of the image to your liking and apply the same settings to every image
• export the images to full size jpegs at 90% or higher quality
• NB. stacking 50 or more high resolution RAW photos is likely to crash your editing software in the next section, so use jpgs for the next step

• this step essentially involves stacking all your jpgs by creating a layer for each jpg and then applying a layer blend mode of Lighten
• Affinity Photo does this well and I found using the VMax setting in the layer blend gives nice results
  • from the menu use File:New Stack then select all your jpgs
  • then in the layers section choose Lighten as Blend mode and consider using Vmax setting
• once this is complete, export the final image as a full size jpeg and a web sized jpeg