Photographing the night sky (1)

Generally, light levels at night are extremely low, and a tripod is essential to hold the camera completely still during the long exposure times that are often required. A shutter release cable to trigger the shutter is an inexpensive extra item and makes any camera movement much less likely.

The best all-round camera for amateur astronomical photography is the single lens reflex (SLR). With this camera, it is possible to change from a normal lens for general pictures of starry skies to a telephoto lens for reasonably detailed studies of the lunar landscape.

Many SLRs feature automatic light measurement and exposure, but this facility is not designed to cope with night-time levels of illumination. Use either a manual model, or one that can be switched to manual operation, and select the T-setting on the shutter control ring. Once the shutter is triggered, it will remain open until the shutter release is pressed again.

There are two techniques for taking pictures of the night sky. The first involves using a stationary camera, the second using a driven camera.

When using the stationary technique, place the camera on the tripod and set the camera to focus on infinity. Next, select an area of sky and then make the exposure. Due to the rotation of the Earth, however, an exposure longer than about 30 seconds will record stars as streaks rather than pinpoints of light. If you include an area of sky containing the celestial poles and expose for about five minutes the resulting photograph will show circular star trails.

A telescope adapter ring, above, allows any single lens reflex camera to form part of a sophisticated recording system of celestial objects. Use the chart, below, as a guide to exposure times.

The Full Moon, above, photographed over the Parthenon, Athens, using a 400 mm lens and a 2-sec exposure. The Full Moon is not the best time for detailed lunar observations because the level of illumination is too high. Some detail has also been lost due to halation - light reflecting back from the base of the film.
 

Exposure recommendations