The photography workbench · 13
A sky full of stars.
A matter of seconds.
See how night-sky exposures turn stars into trails. Compare the simplified NPF rule, the 500 rule and a pixel-motion limit using your lens and sensor settings.
Explore all 15 tools ↗Keep the stars still. Or let them travel.
Untracked camera · tripod8× native-pixel magnification
The inset shows center-frame pixel travel. The scene uses an illustrative star field, not a real constellation map or location forecast.
Loading the night landscape…
- Simplified NPF · equatorial estimate
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- Classic 500 rule · rough guide
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- 2-pixel center-star limit
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- Center-star travel in your exposure
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AI-generated landscape with simulated stars. The preview isolates motion; it does not simulate exposure brightness, noise, focus error, atmospheric refraction, lens aberrations or a tracking mount.
A useful starting point, then a test frame.
The simplified NPF estimate is (35 × f-number + 30 × pixel pitch in µm) ÷ focal length in mm. It is an equatorial rule of thumb, not a guarantee of pinpoint stars. The 500 rule uses 500 ÷ (focal length × crop factor) and can permit visible trailing on modern high-resolution sensors.
The separate 2-pixel estimate uses the Earth’s sidereal rotation, your pixel pitch and the center star’s declination. It estimates motion near the center of an ideal rectilinear image; stars elsewhere can move differently. The NPF estimate stays equatorial when you change declination. All sensor options here use a 3:2 crop, so enter the megapixels remaining in that crop.
Sources: Société Astronomique du Havre’s NPF rule, PhotoPills on star exposure limits, and NASA on sidereal time. Plan a sequence with the timelapse planner.