The Big Dipper sets over the trees and clouds. Taken with a Canon 20Da DSLR camera with a 16-35mm f/2.8 zoom lens working at 35mm at f/2.8 on a fixed tripod with a 30 second exposure at ISO 1600.

You can also shoot beautiful images of the constellations with just a camera on a tripod, such as this shot of the Big Dipper.

1 second exposure at 24mm focal length

2 second exposure at 24mm focal length

4 second exposure at 24mm focal length

8 second exposure at 24mm focal length

15 second exposure at 24mm focal length

30 second exposure at 24mm focal length

60 second exposure at 24mm focal length

300 second exposure at 24mm focal length

Method

Almost all of the methods for shooting constellation photos are exactly the same as shooting star trails. The only difference is that you want to find that sweet spot of exposure length where you expose long enough to record as much faint detail as possible, but don't expose too long so that the stars trail too much.

Again, with digital cameras we have the luxury of being able to make a test exposure and then examine the image and histogram on the back of the camera to determine the optimum exposure.

Not much more is needed than a tripod and camera whose shutter can be kept open for up to 30 seconds. The same suggestions for star trail photography given in the previous section also apply here, only the exposures are much shorter.

Use the self timer or cable release to open the shutter, and make sure the lens is focused on infinity. Set the lens aperture to wide open or stop down one stop. Your exposure should be anywhere from 5 - 30 seconds with a lens in the focal length range from wide angle to about 50mm. Try to use a high ISO, such as ISO 800, 1600, or 3200. Experiment with different settings and see which turns out the best.

If you can put something in the foreground, the picture will be that much more interesting. In the case of the image at the top of this page, I positioned the camera so that there were some trees in the foreground.

As a final special touch, a "fog" filter can be used on the lens. This filter is simply a diffusion filter that is used in portraiture to give a soft-focus effect, diffusing and enlarging the brighter stars and planets in the image. "Fog" filters give a nice effect on constellation photos, making the bright stars that define the shape of the constellation easy to pick out.

This photo did not require a telescope equatorial mounting to track the stars to compensate for the Earth's rotation because the exposures were kept short enough so that star trailing was not objectionable.

Complicated formulas can be used to calculate the length a star will trail based on the length of the exposure, focal length of the lens used and declination of the object photographed. As a rule of thumb, exposures of about 8 - 10 seconds can be made with a 24mm lens for objects on the celestial equator before the trailing becomes noticeable. You can try longer exposures with wide angle lenses or if the camera is pointing more towards the north or south.

The longer the focal length of the lens you are using, the quicker the stars will trail.

Try shooting a series of exposures of 5, 10, 20 and 30 seconds. Generally, if you can see a star or planet with your unaided eye, you can photograph it on a fixed tripod with an exposure of about 10 seconds at f/2.8 with ISO 400.

The examples at right show were taken with the camera on a fixed tripod, all at the same ISO. Only the exposures were changed. They illustrate several different points about photography on a fixed tripod:

Notes

1. Fainter stars are recorded in longer exposures.

2. Sky fog increases in longer exposures.

3. Stars trail more in longer exposures.

4. Fainter detail in extended objects, such as M42 is recorded in longer exposures.

5. The stars move across the sky due to the Earth's rotation and are in a different location in each photograph. We can see this motion, from lower left to upper right, in the longest exposures.

Our goal is to arrive at a compromise exposure that records as much as possible with the least amount of trailing that we can tolerate.