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When shooting starscapes and the Milky Way, you need to choose a shutter speed fast enough to avoid recording too much of the movement of the stars in your shot. This will vary according to the focal length of the lens and camera that you are using. Many astro-photographers use ‘the 600 rule’ as a rough guide to work out the shutter speed you can get away with. All you do is divide 600 by the focal length of the lens – so if you’re using a 20mm