Macro photography is a kind of close-up photography. The classical definition is photography in which the image on film 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 you take a macro photograph of a coin on film. You set the lens for a magnification of 1:1 and move the camera to and fro until the coin is in focus, then take the picture. After you have the film developed, you can place the coin on the film, and you'll see that the coin is 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.

Going back to the coin, you photograph it from farther away. This time, you set the lens to a magnification of 1:4, move to and fro until the coin is in focus, and take the picture. When you compare the coin to the image on film, you see that the real coin is four times as big across as the image. Next, you have a 4× enlargement print made. The enlargement is about 100×150 mm. And when you place the coin on the print, you see that the size of the coin matches the size of the photo of the coin. That is, the image is life-size in the print.

Equipment

There are several kinds of equipment for making the image the required size. These include

• Using a special-purpose lens called a macro lens (some manufacturers call it a micro), having a long barrel for close focusing. A macro lens might be optimized to provide its best performance at a magnification of 1:1.
• Placing an extension tube between the camera body and the lens. The tube has no glass in it; its sole purpose is to move the lens farther from the film or digital sensor. The farther the lens is, the closer the focus (and the bigger the magnification).
• Placing an auxiliary close-up lens in front of the camera's taking lens. Inexpensive screw-in or slip-on attachments provide close focusing at very low cost. The quality is variable, with some two-element versions being excellent. This method works with cameras that have built-in lenses.
• Attaching a telephoto extender between the camera body and the lens. A 1.4× or 2× teleconverter gives a larger image, adding macro capabilities. The image is dimmer, however.
• Using a smaller film or sensor. Placing a rollfilm adaptor on a 4×5 view camera can give a macro image. Likewise, using only the central 1/4 of the area of a digital sensor (discarding the outer 3/4 of the pixels) results in a larger image. Enlarging a small portion of a 35 mm negative or slide also results in a larger image. Photographers might debate whether this is true macro photography, but semantics aside, it can result in a frame-filling photograph that is as large as the original subject.
• Using a bellows attachment between the camera body and the lens to extend the lens to film plane distance.
• Reversing the lens. A special adapter, called a "reversing ring," makes this possible.

Technical considerations

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. Parts of the subject that are even a millimeter closer or farther might be noticeably blurry.

Lighting can be difficult. Some cameras can focus on subjects so close that they touch the front piece of glass in the lens. It's impossible to place a light between the camera and a subject that close, making this extreme close-up photography impractical. A normal-focal-length lens (50 mm on a 35 mm camera) can focus so close that lighting remains difficult. To get more distance between the camera and the subject, photographers use telephoto macro lenses. Focal lengths from about 100 to 200 mm are popular. This permits lighting.

Ring flashes, with flash tubes arranged in a circle around the front of the lens, can be helpful in lighting at close distances.