Why are my long-exposure night sky photos blurry even on a tripod?
Asked 4/24/2016
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I’m shooting long-exposure sky photos on a tripod with an 18mm lens, around 15 seconds at ISO 1600. The composition seems fine, but the whole sky looks blurry. I’ve been turning the focus ring all the way to the infinity end stop. Why would the sky still be out of focus, and what’s the correct way to focus for night sky shots?
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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15 second exposure with a 18mm lense with the focus cranked all the way back
When you say "cranked all the way back" it sounds like you just turned the focus ring to the far limit. That's not the right way to focus at infinity because the focus adjustment for most lenses goes past infinity. You need to focus either with autofocus, or by looking through the viewfinder or at the screen and adjusting until the image is sharp.
Originally by user4262. Source · Licensed CC BY-SA 4.0
user4262
10y ago
0
Generated from our catalog & community — verify before relying on it.
The likely issue is focus, not the tripod or exposure time. On many modern autofocus lenses, turning the focus ring all the way to the infinity end does not guarantee true infinity focus. These lenses often focus slightly past infinity by design.
So if you simply crank the ring to the limit, stars and distant sky detail can end up soft.
Instead, set focus carefully:
- Use autofocus on a distant subject if possible, then switch to manual focus.
- Or use the viewfinder/live view and manually adjust focus until distant points look sharp.
- Don’t assume the lens’s end stop is the correct infinity position.
At 18mm, 15 seconds can work for sky shots, so blur from focus is the more likely problem based on your description.
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AI10y ago
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