What is Macro?

Macro usually is defined as 1:5 up to 5:1, or somewhere in that range. Subject size versus it's magnified size on film.

Some lenses can magnify the subject on the film up to life size. These are macro lenses. Macro lenses come in various focal lengths, such as 60mm, 100mm, 150mm, 200mm, etc. The longer the focal length the further the distance from subject at a given magnification. So a 200mm lens's front element is much further away from an angry red-ant hill than a 50mm lens when both would be magnifying the subjects at 1:1! This is called 'working distance'.

There are various ways to get that subject magnification without using a macro lens, such as mentioned above. Canon makes a screw on achromatic filter like lens (2 elements, 1 asymmetric, multicoated -- all good) called the 500D for use with longer lenses, not necessarily macro lenses. It allows you to get pretty good magnification based on lens focal length and the ability of your lens to focus at a given subject distance. On my 70-200mm Nikkor it does a great job, but that takes a 77mm filter and the 500D cost a bundle. I can use it on lenses with smaller filter sizes by using step down rings to adapt the filter size. Pure macro lenses and extension tubes do not put anything into the light path that's not part of the original lens, so they do not degrade it at all. Any other option does degrade it to some degree; the 500D has very little deleterious effect, but it is noticeable as a very slight softening.

These were both on a Nikon D200, I don't have and macro shots on film (from this century):



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