This is fun!
I've always been rather fond of star trail photos but very rarely get the opportunity. Here in the south east there's far too much light polution and a one hour exposure will give you a bright orange wash and not much else. But there is another way! In the last edition of Practical Photography there was an article on how to combine multiple images to get the same effect. I had a crack at it in my garden tonight and here's the result...
What you do is set your camera to continuous shooting mode, set the exposure to 30 seconds with a suitable aperture (I used f5.6) then use a cable release with a lock on it to set it going. My D300 will take a maximum of 100 shots like this but if I was there as it finished I could immediately set it going again.
When it had finished I put the lens cap on and took a final 30 second exposure as a dark frame for noise reduction, although as I was using ISO 200 the noise was not too bad anyway.
I was shooting in raw as I always do so loaded the shots into lightroom and exported them all as tiffs. Then the final stage is to combine them all into a single image. A very nice chap by the name of Achim Schaller has written a program to do this and it's available free from
www.Startrails.de-Home. You can even watch the trails building up while it runs, which is fun!
When it's finished you can save the result as a tiff, jpeg or bitmap.
When viewed at 100% you can see that the lines are made up of a series of dots...
and this effect gets more pronounced as you get further away from the pole star. But even so, I'm dead impressed as I never thought I could get shots like this from where I live without a major power outage across the whole of Greater London!
Next step is to find something much more interesting than the top of my bay tree for the foreground...
Dave P.