Hallo Mike.
Thank's for Your detailed answer.
I am no star in maths too, but i think 58% is right (anyway my calculator tells me the same
).
I use the Olympus A200 conversion lens, which i like very much, because i don't need any adapter-ring. It has a 49mm thread, the same as my A2. Another advantage is, that you don't have to screw off the lens hood while using the A200.
The disadvantage is the poor magnification of only 1,5x.
The vignetting....well, my A2 has a maximum resolution of 3264x2440. When i make crops with 2560x1920 (again a magnification of about 1,6x) there is no vignetting left, so i am satisfied with my Olympus A200.
But a magnification of 2,2x would be gigantic, maybe i will search in ebay a little bit this night