Principles of Macro Imaging
Introduction:
Macrography is a type of image capture when the image magnification is greater than one. Macro photography is used to photograph small objects as well as small parts of bigger objects. This process lends itself for very interesting images since it largely displays things we do not commonly view or pay attention to. Not only are the results aesthetically pleasing, but there is application for macrography in science, specifically medical, fields. What is normally viewed from a microscope can be photographed for example or further study, for instance.
It’s Not What You Think:
Most people have a misconception of what macrography is. Macro is not simply a close up. In fact a 1:1 reproduction of the object is also not considered a macro image. These scenarios are of close-up photography.
Explaining Macrography:
Most images taken are reduced magnification. This means that the object you photograph is bigger than the resulting image. (This is referring to the image at the image plane in the camera, not to the image display on the LCD screen, computer monitor, or print.) In macro photography, the image is bigger than the object. The maximum image size is the physical size of your film (generally 35 mm) or sensor (half film size or smaller); therefore the object, or part of the object, has to be even smaller. This gives some perspective on what size objects are involved in macro photography. So, how can you take a small object and manage to produce a larger image? Well, the image distance needs to be greater than the object distance. In other words, the distance from the film/sensor to the lens needs to be larger than from the object to the lens. This results in magnification of the object. The amount depends on the image distance.
How to Produce a Macro Image:
With the right equipment, this is fairly easy to produce. With your camera on a copy stand, attach bellows (extension tubes can also be used, but give you less control over magnification). This allows the image distance to be elongated; the controls on the bellows adjust the length easily. A lens is placed at the front of the bellows, and the object at the focal length of the lens.
As mentioned before, the bellows length controls magnification. The proper image distance to produce a desired magnification can be found using the following equations (v is image distance; m is magnification; f is focal length of the lens):
v = (m + 1) * f
Often an arbitrary number can be picked for magnification depending on the desired outcome (such as 3x or 4x). There are times though when a very specific magnification is wanted in to have a small object fill the entire frame. The necessary mag can be found using the next equation where i is image size and o is object size. Then m can be plugged into the previous equation.
m = i / o
Be Careful:
The hardest aspect of macrography is focus. The working distance of a lens in this system is equal to the focal length. Therefore, the object needs to be placed at the focal length of the lens in order to achieve focus. The higher magnification there is, the less depth of field there is. This is a tradeoff that needs to be considered when composing your image. Once good focus is achieved, things that may compromise sharpness need to be considered and isolated. For example, vibrations from a fan in the light source, the camera shifting, or the copy stand moving.
Conclusion:
Though there is structure to macrography, getting the correct magnification, focus, and sharp images will take continuous tweaking. It is a system better perfected through practice. Some objects lend themselves to macro imaging better than others, just as some light sources give you more interesting compositions. Macrography can be a great tool for both art and science; it just takes some experimenting.