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Star Trails Calculator (NPF Rule)
Find the longest exposure you can use before stars start to trail, for pinpoint astrophotography.
Results
- NPF rule max exposure
- 11.6s
- 500 rule max exposure
- 20.8s
- Pixel pitch
- 6.0 µm
The more accurate limit, accounting for your exact aperture and pixel density. Stay at or under this to keep stars as points, not streaks.
The simpler, older rule of thumb. It ignores resolution and tends to overestimate how long you can expose on modern high-megapixel cameras.
The physical size of one pixel on your sensor, derived from its resolution and width. Smaller pixels are less forgiving of star movement.