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Old Jun 2, 2011, 5:51 AM   #1
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Location: Australia, New South Wales central coast
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Default Shooting Star Trails - mini tutorial

G'day all

Several forum members have asked recently about taking long exposures / star-trails, so I have put together these notes. If readers want an extended outline of this material, please PM or email me [ozzie_traveller-at-yahoo.com] for a 3-page PDF on the topic

Star-trails ~ in the suburbs or around the campfire
Back in film camera days it was relatively easy to take star-trail images – just point your camera skywards and set the camera to “B” [Bulb or Brief] and come back an hour later. Unfortunately many digital cameras are limited to an exposure of about 30 seconds, then the noise-reduction process kicks in and over the next 30 seconds while the camera reprocesses the image to minimuse any noise. This has led to digital photographers searching for other methods for taking star-trails.

One enterprising photographer and computer programmer in Germany [Mr Achim Schaller whose web site is “startrails.de”] has developed a program for doing just this, and he has made this program freely & publicly available. It is called “startrails.exe”. The program is easy to use – it stacks lots of images on top of each other so that the bright star movement now becomes visible over the black background of the original image loaded at the bottom of the stack.

This photo is constructed from 550 camera images of 20 seconds each with the camera lens at 18mm
Note – on the computer screen you will see pixellation – it disappears at larger magnifications
NB: To see a “circle” the camera must be pointing at the north or south celestial pole.

How to set up your camera
To take successful star-trails pictures you will need one of two things ~ a camera that has “Bulb” as part of its manual settings, OR a camera that offers “continuous burst”.

Look for a symbol like the infinity sign ... and activate it for continuous shooting.

If you have an up-market camera &/or a dSLR, one accessory available to you is a remote control. When you buy one make sure that it will both press the shutter AND lock down for continuous use. If you have an ordinary fixed-lens digital camera, then it is unlikely that a remote control is available ~ so another method needs to be employed … one that can also be used by dSLR users too, by the way!

Yes – an elastic band wrapped around the camera body, holding (in this case) a small nut which presses onto the shutter release button.

Common problems encountered
If your camera exposures are too short, only the major / brightest stars will be recorded

[these samples are highly magnified]

If your camera exposures are too long, eg: 60 seconds, and the camera's noise reduction [NR] features activate, then you will have a 60 second exposure followed by a 60 second 'null' frame.

This will result in photos that look like:-

So what you need is an exposure time that is a bit of a compromise.
Exposure times of about 15 seconds seem to bring “reasonably good” results for most superzoom cameras, while most dSLRs can use 20 to 30 seconds.

Choosing your ISO speed
For most modern cameras, an ISO of 400 – 800 – maybe even 1600 can be successfully used.

Star Trails for dSLR users.
If your dSLR has a Noise Reduction “cancellation” feature in its menu, then you can select exposure times of up to the camera's maximum – 30 secs or 60secs usually. When activated, the camera will continue clicking away with only a minor pause between frames, rather than the full 30 or 60 seconds gap experienced with other digital cameras.

Using “B” or “Bulb”
Many dSLR cameras come with a “B” setting. Even using “B” + f22 & ISO-200, I have found that the dSLR sensor becomes over-sensitive from 30 minute long exposures and starts to “wash out the image” and you lose much of the fine detail. Your camera might give differing results, so some experimenting is needed.

Moisture [dew] falling onto the camera
You will need to keep an eye on the camera / lens during a star trails exposure and should you note a 'frosting' appearance, carefully wipe the lens with a lens cleaning cloth. While doing this, remember not to shine your torch into the lens – keep your light away from the lens and only use the very faint edge-shine to display the front of the lens.

Processing your images
  • Load all the camera images onto the computer – I have a folder called STARS-TMP for this purpose.
  • Open the Star Trails software and load all the images;
  • Run the program and watch the images as they stack together and build up the contiguous image;
  • Save it as a TIFF image [for post processing if needed]– Resave it as a JPG 100% image [for display];
  • delete the camera images from the computer and save some hard disk space.

Exposed on a night with a full moon + some wandering clouds

Happy Shootin'

Regards, Phil
Has Lumix mirrorless & superzoom cameras and loves their amazing capabilities
Spends 8-9 months each year travelling Australia
Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/
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Old Jun 2, 2011, 10:23 AM   #2
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Join Date: Aug 2006
Location: Tamworth, UK
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Ohhhh Thanks, may give this ago. Not sure I would manage a full circle tho!

Olympus E420, 17.5-45mm, 14-42mm, 40-150mm, 70-300mm and 25mm lens

Kodak Z950
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