Olympus and Panasonic have announced a new, mirrorless format / lens mount based on (and compatible with) Four Thirds. The Micro Four Thirds system uses the same sensor size (18 x 13.5 mm) but allows slimmer cameras by removing the mirror box and optical viewfinder. The new format has three key technical differences: (1) roughly half the flange back distance (distance from mount to the sensor), (2) a smaller diameter lens mount (6 mm smaller) and (3) two additional contact points for lens-to-body communication (now 11 points). Removing the mirror mechanism allows this shorter flange back distance, meaning lenses for the new mount can be considerably smaller than current Four Thirds designs. The format will require framing to be carried out using Live View on either the LCD monitor or an EVF. Existing Four Thirds lenses can be used on Micro Four Thirds cameras using an adapter. Neither company is as yet making product announcements (we expect some more news in this respect closer to Photokina).