Magnification

Definition

Reproduction ratio (magnification) m = image height on the sensor / subject height. True 1:1 macro is m = 1: a 20 mm insect fills 20 mm on the chip. Effective f-number grows with m, and DoF shrinks roughly with 1/m², which is why f/11 at 1:1 is still a sliver. Pupil factor (exit/entrance pupil) tilts front vs rear DoF on retrofocus glass. Focus stacking exists because the formula is cruel, not because you metered wrong.

Calculators that use this

• Optics & depth of field

  Macro Depth of Field Calculator

  Estimate total geometric DoF at close-up magnifications from f-number, magnification, CoC and pupil factor. Use it to decide whether to stack.

• Sensor & focal length

  Field of View Calculator

  Turn focal length, sensor size and subject distance into frame width, height, diagonal and area in metres — useful for lighting and group shots.