Magnification 1:1 mean real life macro. This mean you are capturing scene as big as your sensor size area. Magnification 1:2 is half life macro, meaning you are capturing scene double (or 2 times) your sensor size area. Said your sensor size area is 30mm x 20mm (only for example!), the magnification 1:3 will capture the 90mm x 60mm scene.
Usually (but not always) true macro/micro lens have 1:1 real life magnification. There IS something like magnification 2:1, 3:1 for bigger magnification, but it will need additional tools (for example extension tube(s), close up filter, etc.).
Regards,
Arto.
