How do I choose shutter speed for sharp stars without trails?
Asked 10/25/2015
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I’m trying to photograph the night sky, but even at around 4 seconds I can already see the stars starting to trail. Longer exposures like 10–30 seconds make it worse, but very short exposures don’t gather enough light unless I raise ISO a lot, which adds noise. How can I choose the right shutter speed to keep stars reasonably sharp, and what settings or techniques help with low-light noise?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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The rule of thumb is to shoot at 600/f to avoid star trails, where f is the "focal length" (35 mm equivalent).
For example with a 200mm, 600/200=3s. The minimum shutter speed is 3 seconds.
Anyway, the best approach is to try and eventually change your settings.
Have a look at What times and settings should I use for taking pictures of stars at night and falling stars? and What is the "Rule of 600" in astrophotography? (thanks to mattdm for this one)
Originally by user26456. Source · Licensed CC BY-SA 4.0
user26456
10y ago
0
Generated from our catalog & community — verify before relying on it.
Stars trail because the Earth rotates, so exposure time is limited. A common rule of thumb is the 600 rule: use a shutter speed of about 600 ÷ focal length (using 35mm-equivalent focal length). Example: at 200mm, about 3 seconds is the limit before trails become obvious.
To gather more light, use a tripod, open the aperture as wide as possible, and then raise ISO as needed. One answer suggests ISO around 2000 as a starting point, then adjust after test shots.
If you want cleaner results, take multiple shorter exposures and stack or average them later to reduce noise. If you use a telescope or other tracking mount, you can follow the stars and use longer exposures without trails.
For best results, also shoot on a clear night with minimal clouds, air traffic, and light pollution, and experiment with framing and foreground separately if needed.
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