Macrophotography is close-up photography, usually of very small subjects. Classically a macrophotograph is one in which the size of the subject on the negative is greater than life size. However in modern use it refers to a finished photograph of a subject at greater than life size.
The ratio of the subject size on the film plane (or image sensor plane) to the actual subject size is known as the reproduction ratio. Likewise, a macro lens is classically one lens capable of reproduction ratios greater than 1:1, although it now refers to any lens with a large reproduction ratio, despite rarely exceeding 1:1.
“Macro” lenses specifically designed for close-up work, with a long barrel for close focusing, are one of the most common tools for macrophotography. (Nikon designates such lenses as “Micro” because of their original use in making microforms, but most lens makers use the term “Macro” or “Makro.”)
These lenses are optimized for high reproduction ratios. Most modern macro lenses can focus continuously to infinity as well, using complex focusing mechanisms that alter the optical formula. In most cases these lenses provide excellent optical quality when used for normal photography, although a macro lens may be optimized to provide its best performance at its highest magnification.
True macro lenses, such as the Canon MP-E 65 mm f/2.8, can achieve higher magnification than life size, enabling photography of the structure of small insect eyes, snowflakes, and other minuscule objects.
Others, such as the Infinity Photo-Optical’s TS-160 can achieve magnifications from 0-18x on sensor, focusing from infinity down to 18mm from the object. However, macro lenses with 1:1 or 1:2 ratios are more common, and many of these find frequent use for general photography because of their excellent optics.