The calculation of magnification differences is treated well in a number of texts,1, 3, 4, 5, 7but the formulas are not always presented in their most convenient form. Because of this, many complex schemes have been illustrated2and many different versions have been published.3, 4, 5The purpose of this paper is to present the pertinent equations in a simplified manner and to illustrate them by a specific example, namely, the case of monocular aphakia.