Micro Four Thirds sensors, as used in the Olympus/OM System and Panasonic Lumix G cameras, are about half the size, in area, of APS-C which is, in turn, half the size of full frame. The Micro four Thirds sensor therefore has about one-quarter the area of a full frame sensor. This brings a clear theoretical shortfall in noise control, dynamic range and resolution. It's all down to the smaller sensor area, smaller photosites and generally lower resolution.
But the mistake made by so many is to assume that this immediately plunges the whole MFT setup below some threshold of acceptable quality, whatever that might be. In fact, it's just a question of degree, and not always as simple as it first appears.
