From Wiki-
Macro photography is close-up photography of usually very small objects. The classical definition is that the image projected on the "film plane" (i.e., film or a digital sensor) is close to the same size as the subject.
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 6×4 inch (15×10 cm) print is made, the image is life-size or larger. With 35mm film this requires a magnification ratio of only approximately 1:4, which demands a lower lens quality than 1:1. With digital cameras the actual image size is rarely stated, so that the magnification ratio is largely irrelevant; cameras instead advertise their closest focusing distance.
Macroscopy competes with the digital microscope where a small camera tube can be attached directly to a computer, usually via USB port. Macroscopy also competes with photomicroscopy, and it is much less expensive to achieve high quality images. However, high magnification images are more difficult using macroscopy.
The method is especially useful in forensic work, where small details at crime or accident scenes may often be very significant towards solving the crime. Trace evidence such as fingerprints and skid marks are especially important, and easily recorded using macroscopy. Fracture surfaces from broken products are very revealing using fractography, especially when photographed using glancing light to highlight surface details.Technical considerations
Depth of field
Limited depth of field is an important consideration in macro photography. 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 such as photographing skin cells. Alternatively, more shots of the same subject can be made with slightly different focusing lengths and joined afterwards with specialized focus stacking software which picks out the sharpest parts of every image, artificially increasing depth of field.
Compact digital cameras and small-sensor bridge cameras have an incidental advantage in macro photography due to their inherently deeper depth of field. For instance, some popular bridge cameras produce the equivalent magnification of a 420 mm lens on 35-mm format but only use a lens of actual focal length 89 mm (1/1.8″-type CCD) or 72 mm (1/2.5″-type CCD). (See crop factor.) Since depth of field appears to decrease with the actual focal length of the lens, not the equivalent focal length, these bridge cameras can achieve the magnification of a 420 mm lens with the greater depth of field of a much shorter lens. High-quality auxiliary close-up lenses can be used to achieve the needed close focus; they function identically to reading glasses. This effect makes it possible to achieve very high quality macrophotographs with relatively inexpensive equipment, since auxiliary closeup lenses are cheaper than dedicated SLR macro lenses.Lighting
Ring flashes, with flash tubes arranged in a circle around the front of the lens, can be helpful in lighting at close distances. Ring lights have emerged, using white LEDs to provide a continuous light source for macrophotography.Homemade flash diffusers made out of white Styrofoam or plastic attached to a camera's built-in flash can also yield surprisingly good results by diffusing and softening the light, eliminating specular reflections and providing more even lighting.
