Life-Size Representation in Macro Photography
Focal length, focusing distance, and final output determine how large a camera lens can depict a subject. Understanding these three elements of macro photography and how they affect your photography gives you a foundation for making wise decisions when purchasing macro and close-up equipment, and when creating your shots.
Focusing Distance and Focal Length
A camera lens’s focal length (distance from the lens to the digital sensor, when focused at infinity) is measured in millimeters and determines how a scene is depicted on your digital sensor.
When a 50mm lens is focused on a faraway subject, the lens is 50mm from the digital sensor, and because a 50mm lens is a normal lens (in the 35mm DSLR format), it produces an image that’s similar to how you see the scene with your own eyes. In order to focus on an object that’s closer in distance, the lens must be moved farther from the digital sensor.
At some point, your normal 50mm lens reaches its minimum focusing distance, which falls short of depicting a life-size image of the subject. If you move closer to your subject at this point, you won’t be able to achieve focus on it. The figure provides an example of how focal length and your focusing distance are related.
Moving the lens farther from the digital sensor
The closer you get to a subject (while still achieving focus), the larger it appears on your camera’s digital sensor. Therefore, when it comes to magnifying a subject, you’re limited by the closest distance at which a particular lens enables you to achieve focus.
The idea behind macro photography is to move the lens farther from the digital sensor so that you can move closer to your subject. The farther the lens goes from the sensor, the closer you can get and the more magnified your subject appears in your frame.
This figure reveals the difference between an ordinary 50mm lens and a macro-specific 50mm lens. The macro-specific lens is designed to enable the lens to move farther from the digital sensor, making a 1:1 ratio possible.
The appropriate viewing distance
Do you really need a true macro image? Some photographers argue that the final image — not the magnification ratio behind it — is the only thing worth worrying about. Make sure that you consider the intended usage of an image when determining whether you need a true 1:1 macro ratio to capture the necessary level of detail.
A 1:4 magnification ratio produces an image that depicts the subject at its life-size proportion when printed as a 4x6. If this is the size you intend to make your final print of an image, then everything should work out just fine. Viewers usually look at a 4x6 while holding it. If they wish to see more detail, they can bring the print closer to their eyes.
If that same print were hung on the wall in a gallery or a museum, then the viewer would have a difficult time seeing much detail at all. With a macro 1:1 ratio, the subject is depicted at its actual size in a 36mm x 24mm print. If you blow up that image to 4x6 inches, then your subject appears much larger than life-size when a viewer holds the print in her hand. She can actually stand back a bit and still see detail in the subject. If you blow the print up to 11x14 inches, the viewer will be able to see detail from a pretty far distance, whereas the 1:4 ratio would not be as effective.