Macro is about being able to make small object looks big on the photo, and make big object even bigger on the photo.
That is so-called Magnifying, and macro photograph often refer as rate of Magnification.
Read this:
watch this (Tamron 90mm 1:1 macro with 60mm extension tube)
Then, this (Canon SX30 bridge camera with DCR 250 macro adapter)
Then, a short introduction about 28mm reversed with 60mm extension tube
Thus I have done a experiment with all the methods bellow:
Wiki: small-sensor bridge cameras have an incidental advantage in macro photography due to their inherently deeper depth of field. For instance, some popular bridge cameras produce the equivalent magnification of a 420 mm lens on 35-mm format but only use a lens of actual focal length 89 mm (1/1.8″-type CCD) or 72 mm (1/2.5″-type CCD). (See crop factor.) Since depth of field appears to decrease with the actual focal length of the lens, not the equivalent focal length, these bridge cameras can achieve the magnification of a 420 mm lens with the greater depth of field of a much shorter lens.
Generally, objects in photo (actually on the film inside camera) are far smaller than real size.
For example, you take photo of a car, and car is framed in the photo, definitely the car is far bigger than the camera, but the image of the car in the camera may be just about “2cm” on SLR camera or “1mm” on a compact digital camera.
Thus as you can imagine, if the magnification is 1:1, if a subject like a small apple is as big as your DSLR camera, then if you frame the apple fully on the photo, you can casually call that a “casual macro photograph”, although technically, people often use coin as example.
But just keep in mind, the “film” or the “digital sensor” is far smaller than your camera, so roughly 1/3 of the size of your camera, “casually speaking”.
Magnification calculator list: http://extreme-macro.co.uk/calculators/
the 1:1 (1 to 1 real size ratio) is like when you can clearly frame a 50 cents coin (the largest coin, roughly the size of the film canvas or sensor size) to cover all the area of photo.
Double Lens 50mm-reverse-onto-55mm setup, 10 cm close to coin
Most small compact cameras can focus at that close distance without any problem, but DSLR lens normally can not.
if you can frame into a portion of the coin, that is 2:1 or 4:1 (2x, 4x) magnification;
if by maintaining the sharp focus, you can't frame all it up, then that is around (1:2, 1:4) or (0.5x, 0.25x) magnification.
50mm-reverse-onto-200mm,10cm close to coin; 200mm lens only, 2 meter away;
The calculation of magnification of double lens setup and macro filter setup:
For example, based on the formula:
my pentax M 50mm f1.7 reversed onto my pentax M 200mm f4,
so my total magnification is 4.6x.
use this calculator if your math is not that good