Camera Settings
Camera & Sensor
▼Lens & Exposure
▼Advanced
▼Display Options
Shutter Speed Rules
Click a rule to use its shutter speed
NPF Rule
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Most accurate, accounts for pixel pitch
200 Rule
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Conservative: 200 ÷ focal length
500 Rule
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Classic rule: 500 ÷ focal length
Exposure Analysis
Sky Preview
Note: The preview simulates star trailing and exposure brightness but does not simulate the field-of-view change from different focal lengths. The star field shown is illustrative — trail length and sharpness are accurate.
Rule Reference
NPF Rule
t = (16.856×N + 0.0997×f + 13.713×p) / (f × cos δ)
Original Michaud (2015) formula. N = f-number, f = focal length (mm), p = pixel pitch (µm), δ = declination. Most accurate — accounts for diffraction, pixel sampling, and sensor resolution.
200 Rule
t = 200 / (f × crop)
Conservative rule for sharp stars on modern high-resolution sensors. Good default for APS-C and full frame.
500 Rule
t = 500 / (f × crop)
Classic rule from the film era. Often too generous for modern sensors — may show visible trailing at 100% crop.
Pixel Pitch
p = sensor_width / resolution × 1000
The physical size of each pixel in micrometers. Smaller pixels resolve more detail but are more sensitive to star movement.