Two cameras have caught the imagination this autumn. From Olympus comes the updated OM-D, considered by reviewers to be the best Micro Four Thirds camera for serious photographers. And from Sony we have the revolutionary A7 and A7r, the first full-frame mirrorless system cameras other than the Leica M. Suddenly photographers have lots of choice at a range of price entry points. The choice between MFT, APS-C and full-frame sensors is becoming more difficult. This comparison between the two cameras in Ephotozine looks into the differences.