This can be a very gratifying use of the timed exposure mode. You must use a tripod or otherwise have the camera stabilized, as you will be taking long exposures – possibly very long exposures! You may also benefit from having a remote camera release with a locking feature if your camera has a “bulb” mode. Initially, you will turn your ISO up as high as it will possibly go and set your exposure to perhaps 15 seconds. The idea is that you want to have a very bright scene (not of the sky) so that you can frame your picture. These exploratory photographs are just quick and dirty shots to get your framing right. Once you have decided on your framing, you will need to calculate how long you can keep the shutter open. You can do this by experimentation, but for taking pictures of the night sky, you can use the rule of 600: Divide 600 by the focal length of your lens (don’t forget to multiply your focal length by your camera’s crop factor, if it has one). The result will be the maximum number of seconds you can set your shutter without the stars appearing to be smears instead of dots on the photo. On the other hand, if you want star trails, then the longer the exposure the better! When you have a shutter speed determined, you can experiment with your ISO to get it as low as possible while keeping your shutter open as long as possible. This will result in the best quality night shots. Keep in mind that these are likely to be exposures ranging from 15 seconds up to several hours in time. Anything that emits light during that time will be captured on the image – boats, cars, people with flashlights, even shooting stars or lightning. In some cases this may be desirable, in other cases not. You may be able to take multiple photos of a scene with such light pollution in it and then composite them into one perfect photo once you get home through the use of a photo editing program such as Photoshop or Picasa. You should keep in mind that you will not be using a long exposure in most cases for the moon. A full moon, especially, is actually an object that is in direct sunlight and you will need to use daylight shutter speeds (like 1/800 sec) to take a picture of the moon! Remember that your camera must be on a tripod or otherwise immobilized for this technique.
- For a starscape (no moon visible), you want the widest angle view you can get, probably with an exposure time of no more than 30 seconds, so you will probably need to increase the ISO to allow shutter speeds that fast with only natural lighting (starlight / moonlight). Moonlit areas might require a shorter exposure, depending on the strength of the light. Rule of thumb: Divide 600 by your focal length to determine how many seconds you can leave your shutter open without getting star trails. Starscapes are usually more interesting if the skyline is visible in the frame.
- Find a picturesque scene and set up your camera before sunset to lock in your focus on your subject. Wait for about half-an-hour past sunset, when the night sky is dark, but no stars have yet appeared. Set your shutter speed for about 10 seconds and take the picture. You may need to adjust your shutter time up or down to obtain the best image.
- Go into your yard or to a park in the evening. Set your exposure time to 15 seconds and take a test picture. Adjust your shutter time up or down as necessary to get the best image.