Inverse Square Law
FormulaThe intensity of the beam is inversely proportional to the square of the distance from the source.
mAs₂ = mAs₁ × (SID₂ / SID₁)²
When the SID is increased, the mAs must be corrected in proportion to the square of the distance ratio, to maintain the same exposure at the detector.
Example: SID 100 cm → 150 cm
mAs₂ = mAs₁ × (150/100)² = mAs₁ × 2.25
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