Star Trails
On our recent trip to the Grampians, Neil and I did some late night star trail photography at Lake Fyans.
A few people have asked me how I did it, so I thought I’d share my information with you all.
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With digital cameras and remote shutter releases, it’s fairly straightforward to take star trail photos. I recommend taking multiple shorter exposures and merging them because digital sensors build up heat over long exposures, causing red/purple casts to appear at the edges of the sensor and ruining your shot. Using shorter exposures is a way around this.
For my photos above, the details are below.
Camera Settings
Camera: Canon 40D
Lens: EF-S 10-22mm
Focal Length: 10mm
Aperture: f4.0
ISO: 800
Shutter Speed: 30 seconds x 114 shots & 111 shots
WB: Auto White Balance
Format: RAW
Tripod
Remote shutter release cable
Drive mode: Continuous shooting (burst)
Focus point on the tree (using a torch to illuminate the tree to get the focus point)
Processing
Step 1: (RAW file adjustments to all 114 shots)
Exposure adjustment: +0.9 (to get the exposure level I was after)
Exported the 114 shots as JPEG
Step 2: (Merging photos)
There are a couple of methods of doing the photo merging.
Achim Schaller has written a wonderful Startrails Application to merge all exposures into one JPEG.
It also can create a time-lapse movie ! (see mine below)
Another method is to use Photoshop and combine all layers using “lighten” merging. A handy and time saving method is to use Chris Schur’s Photoshop action.
Step 3: (JPEG Adjustment)
Sharpening (50%)
Noise Reduction (100% colour & luminance)
Celestial Positioning
Depending on what effect you are after, compose your shot accordingly.
For my photo above, I composed the shot using the south celestial pole (see image below sourced from wikipedia) which give the circular effect.
The north and south celestial poles are the two imaginary points in the sky where the Earth’s axis of rotation intersects the imaginary rotating sphere of stars called the celestial sphere. The poles appear directly overhead to an observer at the North and South Pole’s.
For those living in the southern hemisphere, there are a few methods to find the south celestial pole.
Southern Cross Method
The south celestial pole can be located from the Southern Cross and its two pointer stars.
Looking up at the Southern Cross, draw an imaginary line from the two stars at the extreme ends of the long axis of the cross and follow this line through the sky. You can either go four and a half times the distance of the long axis on the Southern Cross in the direction the narrow end of the cross points, or join the two pointer stars with a line, divide this line in half, then at right angles draw another imaginary line through the sky until it meets the line from the Southern Cross. At this crossing point is the south celestial pole.
Magellanic Clouds Method
Using the Magellanic Clouds clouds in the southern sky, make an equilateral triangle, the third point of which is the south celestial pole.
Compass Method
Using a compass, locate true south and point up to an angle equivalent to your latitude.
For example, if you were in Melbourne CBD (-37.814056,144.96168), then using your compass facing true south and looking up at an angle of 37.8° will give you the south celestial pole.
Celestial Movement
Below is a compiled video of all of my 114 exposures from Lake Fyans in the Grampians, showing the celestial movement around the south celestial pole, located at the end of the tree’s branch. (Thanks to “Achim Schaller” for this wonderful application).
You’ll notice too that the light seems to fade on the lake and the tree goes in shadow. This was because the moon was behind us and was fading to the horizon over the hour of exposure. Also the bright light appearing across the lake at the end of the sequence was a car.
For a great article on Night Sky Photography from NightSkyPix, showing it’s not that difficult to get into the hobby, see this link:
How To Photograph Star Trails – We Show How Easy It Can Be To Capture Your First Star Trail Photo