stacking for star trails

One of the things I wanted the new camera for was startrails. And it is easy to do, the one here was made of 120 or so 30 second exposures. You can do as many as your battery/card/patience will allow.

Single star trail image from Kx Star Trails

Obviously the more you do, the longer the trails. I used the fisheye lens (but any wide angle would be fine as well). Set it to f4.5 and set the exposure to 30 seconds at ISO 800. Turn off dark frame (or long exposure) noise reduction if you can. If you live in the Northern Hemisphere and want to capture circular trails around the North Star, sStick the camera on a tripod outside pointing at the North Star (see below for how to find the North Star). Take a single test shot and check that you can see the stars on the exposure. You do not need to worry too much about ISO noise as it will average out, so increase the ISO if you cannot see the stars or detail you want. If the exposure is ok, put the camera in continuous shooting mode, attach the cable release and lock it on, or use an elastic band to jam the shutter down. It should then just keep taking 30 second exposures one after the other for as long as you like. I used jpeg rather than raw to cut down on storage a bit, and also the stacking software does not recognise dng or raw files. If you are nervous, sit beside the camera for as long as you can cope. If you are brave, leave it to it’s own devices and check it from time to time, as it is possible for condensation to form on the lens (especially if you use an uncoated filter). Any pictures affected by your torch can be removed later. If it is cold outside it will mist up when you bring it in, I left mine to dry and warm up before opening anything.

The final star trail from Kx Star Trails

Then all you have to do is stack all the images on your computer. Just ‘averaging’ the images will work, but it tends to create a light sky and very smooth tones, but the star trails are low contrast. For good contrasting star trails use astronomical stacking software. Two pieces of software will do this free. Startrails http://www.startrails.de/html/software.html is pretty good, but does not allow you too much control over the settings. Another easy free program is Picolay http://www.picolay.icbm.de/ . In the file menu, add the pictures. Check through and uncheck or remove any that did not work (eg, the ones where you shone a torch on the lens or any with aeroplane lights if you do not want them). Then just click on ‘Start stacking’ in the stacking menu. It takes a while but writes the result into the same directory as the images. Easy!

There is one trick that StarTrails will do that makes it worth a look. It will also take a stack of images and create a video file from them. Perfect for creating a time lapse movie, whether your subject is of stars or not.