Spot Stars

Calculate max exposure to prevent star trailing (NPF Rule)

Camera Preset

Sensor Size

Megapixels

Focal Length (mm)

Aperture (f/)

Declination (°)

0° = celestial equator (use if unsure)

Accuracy Mode

Default (web/standard prints)Accurate (large prints)

NPF Rule (Recommended)

11.6s

500 Rule

20.8s

400 Rule

16.7s

Recommended

11.6s

Good exposure time for Milky Way photography

Rule Explanations

NPF Rule: NPF Rule accounts for aperture, pixel pitch, and focal length for accurate results
500 Rule: 500 Rule: Simple formula (500 ÷ focal length) - works for full frame only
400 Rule: 400 Rule: More conservative version of 500 rule for sharper stars

Tips & Information

Common Camera Reference