This is one of my images. Although it is not the most interesting of photos as there is no foreground subject to anchor it to the 'real world' It is four, three minute exposures stacked on the computer (I'll give more details of ow to do this further down) Staking images give us great looking star trails, without the digital noise that longer, single exposures would give.
First, decide on your location.
Location is one of the most important factors a to whether you will gain good results from your shoot. Anywhere away from big cities where there will be lots of light pollution should be fine, but the best results are achieved a LONG way from the city, where there is very litte to no light pollution at all. SOme photographers travel to deserts, mountain ranges and national parks to yield these results, although great star trails can usually be achieved closer to home!
Second, Decided on your image.
Decide wether you want to do one single long exposure, or a series of shorter ones then stack them afterwards (which i recommend!) Longer single exposures work best with higher end DSLR's such as the Canon 5dmk2, as you can ramp the iso up quite high with little noise at all, however if you dont have one of these bad boys, I would definitely recommend stacking your images.
Thirdly, Pack your equipment.
ALWAYS take a tripod! I cant stress enough how important this is for perfect composition! Setting your camera up on a wall will almost definitely not give you the image you want, it will give you one you'll have to 'make do' with, which we absolutely dont want. Also make sure to take your lens with the widest focal length (usually 18mm) and your camera, of course. I also take a torch to paint light onto my foreground object which I will talk about later.
Next, set off!
Travel to your spot with your equipment and (hopefully) a friend and some warm clothing.
Depending on your camera, the optimal exposure times may vary. I have a Canon EOS 600d and through some tests have found that my preferred exposure is three minutes. I do a series of 3 minute exposure and stack them at home, for juicy trails with little noise! However a higher, or lower end camera may be able to cope with different exposure lengths.
The aperture of your lens determines how bright your trails will be. For my sample image above, if I remember rightly I used an aperture of 2.8 as it was slightly sharper than my widest of 1.8 yet still let in a lot of light for bright trails. Be careful though, an aperture too wide will pick up stars that your eye cannot see, which may result in having too many trails which could leave your image cluttered and unappealing.
Light painting your foreground is a very useful thing. Take a torch with you to help illuminate your foreground so it will show up in your image and anchor meaning to the image. This technique may take some practice, but should be easily done after a few tries. After pressing the shutter button to take your image, shine your torch on your foreground to brighten it up, being careful to paint the light evenly across it all, otherwise it could lead to bright spots and dark spots which doesn't make for a quality image.
Stacking your images is a very useful tool to know how to do, as it allows for much longer exposure with minimal noise! How exciting. 20 three minute exposures stacked would give the star trails of an hour long single exposure with the noise of a single three minute exposure, get it? Its quite simple to do and is definitely worth a try. The programme I use is called StarStax (http://www.markus-enzweiler.de/software/software.html) and is very simple, quick and effective to use, I highly recommend it. Also if you are stacking images and light painting, only one images needs to be painted as it will show up on the stacked image afterward, if you paint them all the subject will be overpoweringly bright and could render the stacked photograph as unusable.
Thats about it, a brief insight into shooting effective star trails! Hope this has helped, and please post your images onto the blog in the comments as I would love to see them! And if anyone needs inspiration, please check out this Flickr group, some great images in there and they are being updated daily! http://www.flickr.com/groups/startrails/ - thanks again!
