The Rule of 500 is a formula used by photographers to calculate the (shutter speed) for capturing sharp, pinpoint stars without visible "star trails" caused by the Earth's rotation. The Formula:
For cameras with APS-C sensors (like most entry-level DSLRs), you must first multiply the lens focal length by the camera's "crop factor" (usually 1.5x or 1.6x) before dividing.
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It identifies the threshold where the movement of stars across the sky begins to blur into streaks rather than appearing as distinct dots in a long-exposure image. 2. Application and Adjustments
Shutter Speed (seconds)=500Focal Length of the LensShutter Speed (seconds) equals the fraction with numerator 500 and denominator Focal Length of the Lens end-fraction
Example: For a 24mm lens on a Nikon crop sensor (1.5x), the effective focal length is 36mm ( ). The rule would be