Magnification of histologic and ultrastructural photoimages is frequently misrepresented in published reports. “Power,” P, the usual mode of representation of magnification, is defined as the ratio of the distance between two points on the photoimage to that between the same two points on the original specimen, but is idiomatically denoted as xP rather than the mathematically correct xP2 in common usage. In this publication, the definitions of “power” and “area magnification,” the relationship between “original magnification,” “resolving power,” and “empty magnification,” sources of error that may be introduced during processing of papers for publication, and the relationship between magnification and perception are delineated. Practical suggestions, arising from this discussion, for expression of magnifications when publishing photoimages and for dealing with projected photoimages are provided.
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