Now we need to head down a road paved with science. Are you sitting comfortably? The stars in the night sky are in a fixed position, but the earth is rotating, which makes the stars appear as if they are moving across the night sky. It is all very pretty, but the effect is that the long exposures needed to capture the very dim starlight means they start to trail. If you are after a nice long star trail, then that's fine, but often you will want pinpoint sharp stars. To calculate the exposure you can use a series of different equations, relating to the position of the stars in the night sky. To get you in the right ballpark, use the rule of 500:
Rule of 500: t = 500 / f
t = exposure time (s)
f = full frame focal length (mm)
It is likely you will need to adjust the exposure time based on the light pollution and to suit your specific camera set up. There is a lot of trial and error to begin with until you learn how you camera captures the small amounts of light in astrophotography.
ISO, F Number and Other Settings
Choose as high an ISO on your camera that will still give you an image which is acceptable in terms of noise. This varies massively with the camera and sensor. For my Fuji XT-1 I can happily use up to an ISO of 3200, but generally shoot on 1600.
Open your aperture as wide as it will go. Some lenses have very bad vignetting or lens aberrations which don't show up in daylight, but will make stars look like comets at the corners. If you have this problem stop down 1 or 2 stops as that normally helps.
I tend to leave White Balance on auto. I also leave Noise Reduction on. For long exposures, most cameras will take the photograph, and then take a second shot, but this time without exposing the sensor to the light. The camera can then identify any noise being generated by the camera itself. This is known as a dark frame, and the camera then subtracts the dark frame from the light frame, removing some of the noise. It's clever stuff, and you can do this outside the camera in specialist software if you wish.
Post Processing & Advanced Techniques
You are likely to need to post process your image, I use Lightroom. There are number of post processing and advanced techniques to reduce noise and really bring out the subjects, but that's for another blog post. For now, import your image and have a play with the exposure and contrast which will help a lot.
What to Photograph
Here are a few ideas to get you going:
- Orion is particularly good as it is easy to spot
- Cassiopeia - If you capture Cassiopeia, you may well also get the Andromeda Galaxy. You won't be able to see it with the naked eye, but it will show up in your photographs.
- The Moon - The moon is great to photograph. Pop a telephoto lens on your camera and away you go. You will need a faster shutter speed as the moon is really bright compared to everything else. I normally start at 1/60sec.
- General starscapes - If you have a nice landscape you enjoy shooting in the day, try it at night and see if you can fill the sky with stars.
If you do have a go at shooting the night sky, I'd love to see your photographs. Tag me on instagram (@helenfennellphotohgraphy) and use the hashtag #astrophotojoy. Happy shooting and may your nights be forever cloudless!