Macro photography is a kind of close-up photography. The classical definition is photography in which the image on film or electronic sensor is at least as large as the subject. Therefore, on 35mm film (for example), the camera has to 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 a magnification of 1:1.

For example, suppose a photographer wants to take a macro photograph of a coin on film. With the lens set for a magnification of 1:1, he or she moves the camera to and fro until the coin is in focus, then takes the picture. After having the film developed, the photographer can place the coin on the film, and the coin will be exactly the same size as the picture of the coin on the negative or slide.

In recent years, the term macro has come to mean being able to focus on a subject close enough so that when a standard 102×152 mm (4×6 inch) print is made, the image is life-size or larger.

Next, the photographer photographs it from farther away, this time, setting the lens to a magnification of 1:4, again moving to and fro until the coin is in focus, and taking the picture. The real coin is now four times as big across as the image; that is, the image and the coin are in a 1:4 relationship. If a 4× enlargement print (about 100×150 mm) is made, the size of the coin will match the size of the photo of the coin. That is, the image is life-size, or 1:1, in the print.