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Excerpt from Field Guide to Geometrical Optics
The longitudinal magnification relates the distances between pairs of conjugate planes.
These equations are valid for widely separated planes. As the plane separation approaches zero, the local longitudinal magnification is obtained.
Since m varies with position, longitudinal magnification is a function of z and z'.
|The use of reduced distances and optical angles allows a system to be represented as an air-equivalent system with thin lenses. Consider the example of a refracting surface and its thin lens equivalent. Both have the same power φ.|