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Garry Black Photography

Question:

What technique is used to photograph star trails? How long does the exposure have to be in order to get those long arcs of light across the sky?

Answer:

Photographing star trails is not as easy as you might think, well technically it's pretty easy but in practice it isn't. First of all you will have to be far away from any light pollution, so taking these shots in or around a city is right out of the question. So you're going to have to be out in the country, preferably in the middle of nowhere, and then you're going to have to be there a few hours. I've taken all of my star trail shots when I've been camping. I set up the camera for the shot, start the exposure, and set the alarm clock and go to sleep for a few hours.

Now for the easy part, well relatively easy. This is the equipment that you will need to photograph star trails:

1. Tripod
2. Camera with bulb setting
3. Locking cable release (mechanical or electronic)
4. Small battery powered fan and holder
5. Wide angle lens
6. Flashlight to see what you're doing when you're setting up the camera and also that you don't trip over a log on your way back to your campsite.

Decide on a composition, now since you want to get long arcs of light you will need to include the North Star in it. You might want to include some foreground objects, such as trees, mountains/hills, or the horizon line of a lake. These provide a base or reference point for the image.

To find the North Star you have to begin by finding the Big Dipper, once you've found it find the two stars that form the outer lip (the side farthest from the handle) of the dipper. Now mentally extend the line through those two stars starting from the outer bottom star to the outer top star of the Big Dipper's bucket. Extend this line about five times the distance between the two stars of the Big Dipper. You will find the North Star along this line; it's the first prominent star that you'll see. The North Star also forms part of the Little Dipper's handle.

The stars appear to rotate around the North Star, in reality it's caused by the rotation of the Earth. It's easy to see why early man thought that the universe rotated around the Earth. The farther your image is away from the north star, the straighter the star trails will look.

A problem that I've frequently encountered while photographing star trails, is that while my camera is outside at night condensation forms all over it, including the front of the lens. A solution to this problem is to keep the air moving in front of the lens. That's what the small battery powered fan is for. Set it up so that it is physically just outside of the field of view, you can shine the flashlight on it. Look through the viewfinder, if you can't see it, it won't be in your image.

I use either 50 or 100 ISO speed film; you don't really need fast film for these shots. Set the aperture on your lens as far open as possible (f2.8, f3.5). Open the shutter on the bulb setting of your camera with a locking cable release with either a mechanical or electronic release. For the exposure time, the longer the better! The longer you leave the shutter open, the longer the star trails will be. I've found that somewhere between 4 to 6 hours is optimum.