Something I have wanted to do for some time is to photograph star trails. You would think that it would be as easy as putting your camera on a tripod, aiming perhaps at the north star, putting the camera in "B" mode, then using a remote release to start and stop the exposure.
Surprisingly, you don't actually do this if you want best results. What you do is take a series of exposures and use special software to composite them together.
General recommendations are to use fast ISO settings (such as ISO 1600) and the widest possible lens apertures. Wide lenses are the best choice.
It is a good idea to do this on a moonless night, at a place far from city light. It is also worth considering a good location that provides an interesting setting, or sense of place. Something like star trails above the Golden Gate Bridge or the Washington Monument or the Devils Tower, or a dumpster in a nearby alley.
Also bear in mind that long exposures will dramatically run down camera batteries I was eager to capture some star trails on a backpack trips, but decided against it because of this -- and also I forgot my remote release, which would have made it tricky.
Take a headlamp, or at least a flashlight, better yet take several. A good tip is to first do a dry run at home in good light.
Put the lens cap on and take a dark frame (or several) for noise subtraction later. Set the shutter for continuous shooting (like machine gun mode for sports), and set the exposure for something like 30 seconds. Doing this means you can use an ordinary remote release and don't need a fancy timer remote (though they have their place). The camera will take one 30 second exposure after the other. A 2.5 hour session will yield 300 exposures. An hour exposure will yield good results: Here is a checklist:
Use lightroom, set light and dark levels, apply the same for all. Export all the image as Jpeg files. Individual frames (with planes or people walking in front) can be deleted.
There was a collection of demo images that I used. They were taken using a Canon 30D camera (and 8 megapixel camera), using 30 second exposures taken one immediately after the other. The camera was set to ISO 800, and a 12mm lens was used at f/4.5. The demo provides 20 images and 5 dark images, all as jpeg files. The dark files were taken with exactly the same settings as the star files, the only different no doubt is that they were taken with the lens cap on.
Tom's Photography Info / tom@mmto.org