The Milky Way
Capture the light show at the centre of our galaxy
The stars we see in the night sky are from our local galaxy – Andromeda. Our solar system is 26 thousand light years from the central galactic core, and from our view, individual stars within it become indiscernible – combining into a milky glow that gives the Milky Glow its name.
These pinpricks of light are very faint, which makes photographing it particularly challenging. To capture the weak light you’ll need to be somewhere very, very dark as light pollution from cities and other artificial light sources will easily overpower it. And to capture the light you’ll need to set an exposure that floods your sensor with as much light as possible during the time that the shutter is open.
The 500 Rule
The exposure time itself is limited due to the movement of the stars in the sky (or more correctly, the rotation of the earth). This is traditionally determined by the ‘500 rule’, where you divide 500 by the focal length of your lens to calculate the longest shutter speed you can get away with. So with a 16mm lens that works out at 30 secs (500/16 = 31.25). If you’re using a DX-format Nikon, base this on the effective focal length (EFL) of your lens – so a 10mm lens multiplied by the 1.5x crop factor gives a 15mm EFL. A more practical method is to start at 20 secs and adjust until you find the longest exposure before trailing starts.
You’ll also need to set a wide aperture to enable as much light to reach the sensor as possible – f/2.8 or faster is ideal. But even then, you’ll need to boost the brightness of the captured image by setting an ISO of around 4000.
A shoot of the night sky alone lacks context – so some kind of foreground interested is essential. But this introduces an additional problem; the high ISO, necessary to capture the stars, leads to image noise, which will be particularly noticeable in the foreground. The solution is to capture a second frame for the foreground shot at a much lower ISO but with a correspondingly longer shutter speed – often several minutes long.