The new Olympus OM-D E-M1 represents a fusion of two distinct systems: Four Thirds and Micro Four Thirds. Olympus did develop a new Four Thirds DSLR, the E-7, but then decided to drop the project when they realised they could incorporate the best parts of both systems into one single camera. The body remains compact but includes all the features we professionals need, and works seemlessly with all Olympus Zuiko and M.Zuiko lenses.
The autofocus capabilities of the E-M5, the former Olympus MFT flagship camera, has always been bi-polar: super fast in AF-S mode, but limited in AF-C (continuous). An adapter for FT lenses was already available but the autofocus was very slow. So one of the main challenges in developing this new camera was to build a body that would satisfy both FT and MFT users. To achieve this, Olympus had to build a new sensor with a hybrid autofocus system that incorporates both contrast and phase detection capabilities.