Macro photography refers to close-up photography; the classical definition that the image projected on the "film plane" (i.e film or a digital sensor) is the same size as the subject. On 35 mm film (for example), the lens
must have the ability to focus on an area at least as small as
24×36 mm, as this is the size of the image on the film. This is known
as "life-size magnification" or simply 1:1. In recent years, the term macro has been used in marketing material to mean being able to focus on a subject close enough so that when a regular 4×6 inch
(102×152 mm) print is made, the image is life-size or larger. This
requires a magnification ratio of only approximately 1:4, more easily
attainable by lens makers.
