Night sky photography requires some specific equipment and techniques.
- You must have a tripod because whether you are shooting digital or film you will be exposing the image for very long periods (in photography a long period is pretty much anything over half a second).
- You must have a camera that is able to have long exposure times.
- You must be able to control the lens opening (the “f-stop” or “aperture”).
- You must have a wide-angle setting for the focal length.
- You must have a very high ISO film or be able to set the ISO on your digital camera to something like 800 or 1600.
- (Optional) If your camera has a built-in automatic noise processing function you must be able to turn it off
The reason for all of this is to capture as much light as possible without having the stars turn into fuzzy blobs. With the settings I’ve described above you’ll get a lot of light into the camera and still have pin-point stars. Anything over 30 seconds or if you zoom in to telephoto you’ll start to see star streaks/blobs since the Earth is spinning the whole time, making the star field traverse across the sky.
This night sky image of the stars above Anza Borrego Desert State Park was taken with my Canon 40D with my EF 24 – 105 mm f/4 L IS USM lens. The lens was set to f5, the exposure was 20 seconds (the 40D has a maximum exposure time of 30 seconds, exposure times higher than that must be executed in Bulb mode). The f-stop is slightly smaller than full open in order to reduce/remove distortions caused by the very edge of the lens optics. An f/5.0 setting “chops off” the light at the very edge and sharpens the image at the expense of losing a little bit of light.
If you want to take those super-cool pictures that show the stars as long circular streaks then you are looking at very long exposures – 30 minutes or an hour or even more. In that case you can adjust some of the other parameters so that the overall amount of light entering the camera is less per second. The stars themselves are bright points and get detected OK anyway.
This image of streaking stars above Death Valley is about 30 minutes long at f5 with an ISO of 400. A higher ISO in this case records too much background light in the sky.
Exposures like this are where film cameras still shine since in many upper-end digital cameras long exposures will trigger the camera’s built-in noise reduction algorithm which requires as long a time to process as the exposure, so a 30 second exposure requires 30 seconds more of processing, so an hour exposure is a two hour total process. You can get twice as many exposures (or be done in half the time) than with a digital camera in those circumstances. If you can turn off the in-camera noise processing you should consider doing so. Photoshop CS3 RAW processing has a noise reduction feature included as way to reduce or eliminate noise artifacts from long exposure images.