Macro photography is a kind of close-up 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.
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. Some macro lenses, like the Canon MP-E 65 mm f/2.8, can achieve even better magnification— up to 5:1 macro, bringing the structure of small insect eyes, snowflakes, and other miniscule but detailed objects into striking focus.
- 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). Also, less light will reach the film or sensor, therefore a longer exposure time will be needed.
- Using a bellows attachment between the camera body and the lens to extend the lens to film plane distance. Similar to an extension tube, but adjustable.
- 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. As with an extension tube, less light will reach the film or sensor, therefore a longer exposure time will be needed.
- 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.
- Reversing the lens using a "reversing ring". This special adapter attaches to the filter thread on the front of a lens and makes it possible to attach the lens in reverse. Excellent quality results up to 4x lifesize magnification using fairly cheap, "standard" (not specially designed for macro) lenses can be produced. For cameras with all-electronic communications between the lens and the camera body, such as Canon EOS, reversing rings are available which allow all camera functions, including open aperture metering, to be used. When used with extension tubes or bellows a relatively cheap but highly versatile macro system can be assembled.
- Reversing a lens of lesser focal length in front of a normally mounted lens using a very inexpensive "macro coupler," which uses two male filter threads to join lenses. This method allows most cameras to maintain the full function of electronic communcation with the normally mounted lens for features such as open-aperture metering. Magnification ratio is calculated by dividing the focal length of the normally mounted lens by the focal length of the reversed lens (i.e., when a 50 mm lens is reverse mounted on a 200 mm lens a 4:1 magnification ratio is achieved). The use of automatic focus is not recommended due to the extra weight of the reverse-mounted lens. Attempted use of automatic focus with this technique could result in damage to the camera or lens.
Technical considerations Edit
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. Due to this, the use of a microscope stage is highly recommended for precise focus with large magnification such as photographing skin cells.
Camera movement can be a problem at extremely close distances due to the paper-thin Depth of field. Use of a tripod or other camera support can be extremely helpful, and is essential when lighting conditions require slow shutter speeds. Tripods and other supports can be equipped with a Macro rack, a device that allows fine movement of the camera toward or away from the subject along the lens axis without moving the tripod.
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. More recently, ring lights have emerged, using white LEDs to provide a continuous light source for macrophotography.
- This article contains information originally taken from the Wikipedia article "Macro_photography". You can see the authorship and revision history of that article here.
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