In photography (especially macro- and close-up photography), magnification refers to the magnification of the object (which is being photographed) onto the sensor/film.

Magnification is usually expressed as a fraction delimited by a colon with the first number indicating the height of the image, and the second the height of the object. Thus 1:1 indicates life-size replication; 1:3 that the object is projected at 1/3 size onto film/sensor; and 5:1 that the height of the image is 5 times real-life -sized.

Technically, the formula for computing magnification is:

Formula for computing magnification

In this formula:

  • M is the ensuing magnification
  • d is the distance from the lens to the image/object (subscript i or o)
  • h is the height of the image/object (subscript i or o)
  • f is the focal length

N.B! Considering that the ‘lens’ in physical terms is not a single point, computation of magnification based on known lens traits (focal length, MFD, lens size) is not obvious.

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