By definition Macro photography relates to the apparent size of the subject when printed as full frame contact sheet (remember those from the film days?) compared to the same subject measured in real life.
If a detail in life is measured to be 10mm across (left to right) when photographed as a "Macro" the detail should be 10mm across when printed as a contact sheet. Considering my d200 sensor is 23.6mm wide this detail would have to fill the frame almost halfway to be a true Macro image capture. -I say it in this manner because I'm not going to make a 23.6 image on the PC just to measure my details all of the time. Besides CS3 Extended has this very measuring feature built in!
However, camera sellers and manufacturers are now saying that the subject should be life size or greater across a 4x6 print! Well, that's cheating in my book!
True Macro photography is harder than it seems for many of our cameras and lenses because if we try and get closer to a small subject in order to capture a fine detail we often find that the lens focus barrel runs out of travel before we can get to this actual size capture.
The laws of optics actually allow
any lens system to do this sort of thing but the internal lenses would have to move away or closer together too much to make it a use-able lens for any other purpose. -For many lenses, all you'd have to be able to do is be able to
continue to rotate the outermost lens so it moves away from the camera body toward the subject. I have a manual focus
55mm f/2.8 Micro Nikkor lens that is made for Macro work. Even though this lens barrel only rotates almost one full revolution, the lens itself extends 1.5 inches in length!
Taking it a step further I'd like to add that traditionally, the term "Macro" refers to the range of detail reproduction ranging from actual size, called a
Reproduction
Ratio of 1:1 to a magnification of up to 10x actual size (
RR = 1:10). The term "Micro" is reserved for image captures that go beyond a 10x magnification.