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).
So Olympus can't stick with their own designed-for-digital-from-the-ground-up lens mount just a few years after introducing it? While "old" lenses can be used on the new mount, obviously lenses for the new mount will be incompatible with "normal" 4/3 cameras. Fragmenting the small market into several incompatible sub-markets is hardly the way to get wider support for the much touted "standard".
* Same Four Thirds sensor size (18 x 13.5 mm)
* No mirror - so the cameras will not be SLRs
* Flange back distance half that of Four Thirds (20 versus 40 mm)
* Lens mount diameter 6 mm smaller (44 versus 50 mm)
* Contrast Detect AF is implied (passive would require an external sensor)
* Lens to body electrical contact points up to 11 from 9
* Lenses of same focal length and maximum aperture considerably smaller than Four Thirds
* Enables slim and compact lens-interchangeable digital cameras
* Lack of mirror well necessitate a high quality EVF (or non-viewfinder design)
* Current Four Thirds lenses can be used with an adapter
* Enables seamless switching between still and movie shooting