Reciprocal Rule
ExposureThe minimum handheld shutter speed to avoid camera-shake blur equals 1 divided by the focal length.
The minimum handheld shutter speed to avoid camera-shake blur equals 1 divided by the focal length. For a 50mm lens on APS-C: minimum shutter = 1/(50×1.5) = 1/75s. High-resolution sensors require a stricter version: 1/(√(MP/12) × crop × FL).