Weather conditions were perfect the other night for some Star Trails photography and as I had never actually tried this technique before I thought it was a good chance to have a go. I used a Canon 40D camera and a Tokina 11-16mm lens but so long as your camera can take individual long exposure shots over a period of time then you should be good to go (if you wanted to). DLSRs are not really suited to keeping the shutter open for a long time as you end up with hot spots on the image, so a more practical solution is to take a series of shorter exposed images over time.
-Camera which can take continuous long exposure images over time
-Charged camera batteries
-Tripod – essential to keep the camera steady and pointing in the same direction
-A clear night
-Remote release used to keep the shutter release open – else you have to press the shutter release each time to take a shot
-Torch – basically to see where you are going in the dark ;-)
-Some foreground object, a tree perhaps or the top of a building .. etc
I tested the process in my back garden with the top of a tree as my foreground interest, then with the camera on a tri pod I set it to an exposure time of 30secons, ISO 400, F5.6 and auto white balance. Focusing on the stars was done manually and I had a cable release for starting the shoot. After a few test shots to check the settings I pressed the remote and set it to hold the shutter release; so although the camera is capable of taking 6 shots a second it was now taking 1 shot every 30 seconds :-) I then left it alone for just over an hour and ended up with 100+ photos. I shot in RAW and used a 2gb card.
Note: When I decided enough was enough I shone the torch into the tree for the last two exposures, this brought some light to the foreground. Then I released the shutter and stopped taking pictures. The last thing you have to do is put the lens cap back on and take one more photo, will tell you why in a moment.
Armed with all those photos I converted them from RAW to JPG (also tweeked the colours slightly) and then used startrails.exe (free software) to stitch all the photos together. This is possible in photoshop, or a similar package but would take ages, where as with startrails you point the software to the folder containing your images and it does the rest. Now, the image you took with the lens cap on — this is known as the “darkframe” in Startrails and useful for reducing image noise.
You can see the first result on my Flickr page to the left hand side, however I wanted to share the process.