I have to confess, I don’t really know the night sky too well, I only know some of the more famous constellations and where you can find certain planets but that’s about it. However I’ve always had a fascination with astronomy and I am always on the lookout for significant events in the astronomical calendar. This month saw the annual Geminids meteor shower one of the most frequent meteor shows of the year with up to 100 meteor showers visible per hour at its peak. I decided to view the Geminids from my back yard on a cold cloud free night which seemed ideal for night time photography as well.
The images below show what can be achieved with a relatively straight forward set up. A tripod is a must along with a shutter release cable or similar remote trigger. Which comes onto two important considerations when photographing the night sky; 1) How long to expose your image and 2) digital noise.
I used the “500 rule” as a guide to decide on the maximum length of your exposure to ensure stars were free of blur. Realistically there is always going to be some star blur especially noticeable if you zoom in at 100% crop.
Maximum exposure time = “500 rule” / focal length of lens
Using a shorter exposure and a low ISO setting ensured my images were relatively noise free. This isn’t always possible of course however and I generally find an ISO setting of up to 800 and even 1600 perfectly acceptable. Modern digital sensors do a remarkable job of minimising any noise in low light.
Using digital manipulation software such as Adobe Photoshop or Lightroom allowed me to make a few tweaks to greatly enhance the final image. First of all I had to tackle image noise. I reduced the noise by adjusting the noise luminance scale in Lightroom, increasing it to about + 40. Next I adjusted the colour balance to a cooler 3800 kelvins. Some suggest going even colder to around 3000k, although I personally think this is too blue. I then increased the image contrast and adjusted the other basic sliders such as shadow and highlights until the image appeared more striking. The clarity slider was then adjusted to about +80 to make the stars really shine and the sharpening tool was also used a moderate amount. These basic adjustments really help an image of the night sky stand out by enhancing the stars against the dark sky. It is completely subjective so it is worth experimenting with the levels to see what works best for you. There are plenty of excellent resources on the internet dedicated to post processing night sky photographs.
My top tips:
- Choose a cold, cloud free night ideally around new moon.
- Use a sturdy tripod, mirror lock up and a remote shutter release to prevent unintentional blur. Most modern cameras feature a ‘bulb’ long exposure setting.
- Ensure you wrap up warm and have a torch handy with you.
- Use a wide angle lens with a wide aperture. A 14mm-20mm is ideal for night sky landscapes.
- Manual focus at infinity. Focusing is particularly difficult so it helps to use your camera’s “Live View” and your widest aperture to focus.
- Use the “500 rule” as a rule of thumb for calculating your exposure, to ensure your stars remain sharp. Remember to factor in any crop magnification to your calculation (Nikon DX 1.5x, Canon APS-C 1.6x).
- Use a high ISO setting - as high as ISO 1600 works very well and allows you to capture images you would otherwise not be able to. A lower ISO setting minimises image ‘noise’.
- Complete some post-processing concentrating on noise luminance slider first then the others. Adjust the colour balance to your liking and ramp up the clarity slider!
- Get to know the night sky, study maps or use a phone app. Polaris ‘North Star’ is an obvious starting point for star trails.