For example, when producing a 6×4-inch (15×10-cm) print using 35 format (36×24 mm) film or sensor, a life-size result is possible with a lens having only a 1:4 reproduction ratio.
[9][13] In the digital age, a photograph is more practically defined as macro when an object measuring 24 mm or less either matches the frame's height or is larger.
[14] The term photo-macrograph was proposed in 1899 by W. H. Walmsley for close-up images with less than 10 diameters magnification, to distinguish from true photo-micrographs.
(Unlike most other lens makers, Nikon designates its macro lenses as "Micro" because of their original use in making microform.)
Most modern macro lenses can focus continuously to infinity as well and can provide excellent optical quality for normal photography.
The further the lens is from the film or sensor, the closer the focusing distance, the greater the magnification, and the darker the image given the same aperture.
The possible quality is less than that of a dedicated macro lens or extension tubes, with some two-element versions being very good while many inexpensive single element lenses exhibit chromatic aberration and reduced sharpness of the resulting image.
These lenses add diopters to the optical power of the lens, decreasing the minimum focusing distance, and allowing the camera to get closer to the subject.
Lenses such as the Nikon PC-E and Canon TS-E series, the Hartblei Super-Rotator, the Schneider Super Angulon, several Lensbaby models, the Zoerk Multi Focus System, and various tilt-shift adapters for medium format, allow the use of tilt in cameras with fixed lens mounts.
When used with extension tubes or bellows, a highly versatile, true macro (greater than life size) system can be assembled.
This method allows most cameras to maintain the full function of electronic and mechanical communication with the normally mounted lens, for features such as open-aperture metering.
[28] For example, the 12 megapixel Micro Four Thirds Panasonic Lumix DMC-GH1 camera with a 2× crop sensor only requires a 1:2 reproduction ratio to take a picture with the same subject size, resolution, and apparent magnification as a 12 megapixel "full-frame" Nikon D700 camera, when the images are viewed on screen or printed at the same size.
This makes it essential to focus critically on the most important part of the subject, as elements that are even a millimetre closer or farther from the focal plane might be noticeably blurred.
Due to this, the use of a microscope stage is highly recommended for precise focus with large magnification, for example when photographing skin cells.
For analog film cameras light scanning photomicrography (LSP) has been used to overcome depth of field limitations.
It is difficult to place a light between the camera and a subject that close, making extreme close-up photography impractical.
Many macro lenses are characterised by a high amount of chromatic aberration, especially when using reversed-lens, extension tube or close-up lens.