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How does this work at macro level (with macro lenses)... Does magnification ratio changes for macro setting...
This is more of theoretical question. If it changes, no use (as magnification can reduce only). If not, just a pieces of glass in between....
Magnification ratio is based on the size of your subject relative to your capture media, so a macro lens that is designed to go to 1:2 on 35mm FF camera will go 1:1.5 on a APS-C sensor (because you've effectively cropped away part of the image the lens was designed to produce). Since the speed booster changes the effective focal length, and therefore the smallest magnification ratio that can be achieved, your 1:2 macro will be closer to a 1:1.8ish.
If the smallest possible magnification ratio with a common SLR macro is what you're after, take the Speedbooster out of the equation and get a native 1:1 macro like the Contax S 60.