Photographing the Night Sky

By Vern and Barbara West

On a recent nighttime shoot of the Comet C2020 F3 / Neowise, we had a crash course on remembering all the ins and outs of photographing the night sky.

One of the first steps we do is try to get to our location during the daylight hours and set our focus on some distant object. Next, switch the lens focus to manual. Use Gaffer’s tape on the focus ring of the lens and the zoom ring (if applicable) to keep from accidentally moving them. After the sun goes down, especially when there is no moon, focusing becomes difficult, but if the moon is up you can usually secure focus on it. If you change composition or zoom in or out you must reset focus which can be challenging in the dark.

On some lenses, the manual focus selector is difficult to operate, especially in the dark. Therefore, an alternative to setting the lens to manual focus (if your camera has the capability) is to set it to rear button focus. This allows you to more easily refocus on the moon or a distant bright star/planet during the session.

In the dark it can be difficult to find the buttons and controls on the camera. Practice and learn your camera well. Even in the daytime try to make adjustments without looking at the camera. This makes it much easier to work your camera at night, but always have a small flashlight at the ready (preferably a red light or one that has a very dim setting to help preserve your night vision).

Once you start photographing there are other things to watch out for.

The first image shows an airplane flying through the composition. The plane appears as a streak of light when the shutter speed is slow. It is easy to concentrate on your subject and not notice a plane.

When your shutter speed is slower than 1/4th second or so, using mirror lockup is a necessity on a DSLR. The mirror moving and you pressing the shutter button causes camera vibrations that cause the stars to be fuzzy or even appear to streak. If you are using a mirror-less camera this is not a concern.

To minimize these vibrations, even with mirror lockup, use a cable release. If you don’t have a cable release you can set your shutter to a 2-second delay to give the vibrations from touching the camera time to settle down.

The second image shows what happens if the shutter speed is too slow. The earth is rotating in relation to the stars and the result is the stars and comet are elongated. A rule of thumb is to divide 500 by your focal length. This number is the length of time you can have the shutter open without causing the stars to streak. For example, 500 divided by 200mm lens equals 2.5 seconds. If you use any shutter speed faster than 2.5 seconds the stars will not streak.

Of course, sometimes you want the stars to streak into long arcs, but that is a subject for another blog.

Night photography is always a juggling act to get a good exposure without raising the ISO so much as to cause digital noise or slowing the shutter speed and causing the stars to streak. Some cameras do a better job of minimizing digital noise at high ISO settings. All digital cameras have a setting to reduce noise at high ISO. It’s usually called something like High ISO Noise Reduction.

Long Exposure Noise Reduction is another setting on cameras that helps reduce digital noise associated with longer shutter speeds. Digital noise is random, so when using the Long Exposure Noise Reduction setting the camera will take a second image without raising the mirror or opening the shutter. The two images are combined in the camera software. The result of this is a doubling of the time between shots but reduction in noise. If you have a 5-second exposure, the camera takes a second 5-second image so it takes 10 seconds before you can take another exposure.

The last image shows not only an airplane but the headlights of an automobile intruding in the image. Be aware of other things getting in the image. This is true not just for night time photography but for daylight photography as well. “Hand of Man” is not always accepted by Publishers/Editors and it can detract from the “essence” of the image you want to capture.

Vern West and Barbara West are Photo Guides for Arizona Highways PhotoScapes.