20130814_0001-EditWe’ve had a couple of clear nights recently and with the prospect of seeing the Perseid meteor shower I’ve been spending some time in the garden of an evening. I didn’t have much joy – maybe two or three over the course of a couple of nights.

While I was out there, I decided to set the camera up and have a go at star trails. I was mainly aiming to try out the techniques and see what happened. I figured the level of light pollution where I live would rule out getting anything worthwhile, and I was pretty much right.

20130813_0007I started off with a few 30 second exposures, such as the one on the left here, just to get a feel for what I could capture. At that duration, with the aperture wide open, the stars are quite clear but the street light is starting to become obtrusive. The camera has picked up far more stars than were visible with the naked eye.

I tried the stack approach of taking a series of exposures of around five minutes each with a view to combining them in Photoshop. Five minutes is long enough to capture some movement in the stars, and as long as the gap between exposures isn’t too long it should be possible to get continuous trails. Unfortunately none of those experiments quite came off, but I’ve learnt some useful lessons.

Finally I decided to go for a really long exposure – almost 25 minutes (I was aiming for half an hour, but it was cold and I wanted to go to bed!). As expected the sky was getting really bright from the ambient street lighting and the sensor noise was building up. Still, with a little judicious tweaking of levels it was possible to see the stars rotating around the pole star (neither of these work well at thumbnail size, just click for a larger version).

For an experiment it worked out reasonably well, and I now have a better idea of what to do if I can find the combination of a clear night, no moon and darker skies a little further away from civilisation.

 

3 replies to “Experimenting with star trails

  1. Richard Francis says:

    I actually like how bright the foreground is. It almost disorientates me to whether it is night or day. Great picture. But there’s something missing…

  2. sean says:

    That would be posted on the other site… and I don’t think I can get a model to stay perfectly still for half an hour in the cold anyway!

  3. Dave Worton says:

    It’s a classic and so many uses for a good star trail shot. Apart from meteor detection, you’ve got the best way of finding true north, detection of colour bias and noise in long exposures and nowadays you can even play spot the geo- stationary satellite (the ones that don’t leave a trail). Who wouldn’t want to try all that? But you have to be a bit careful about which meteor shower you are trying to catch 😉

    http://xkcd.com/1249/

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