500 Rule Calculator
Maximum shutter speed for sharp star photography
Calculate Maximum Exposure
20.8s
500 Rule
12.5s
300 Rule (Sharper)
8.3s
NPF Rule (Strictest)
About These Rules
500 Rule: Classic rule. Max seconds = 500 / (focal length × crop factor). Shows slight trails on high-res sensors.
300 Rule: More conservative. Better for modern high-resolution cameras.
NPF Rule: Most accurate. Accounts for pixel size: (35 × aperture + 30 × pixel pitch) / focal length. We estimate using typical values.
Tips for Astrophotography
Use a sturdy tripod and remote shutter. Focus manually on a bright star using live view at 10x magnification. Use wide aperture (f/2.8 or wider) and high ISO (1600-6400).