There is an interesting difference between film and digital. In the film days, all 35mm cameras took the same size of film. That meant that better results could be obtained by upgrading to higher quality film. Newer, more sensitive film meant being able to use your old camera in new (darker) conditions. The invention of colour film didn't necessitate everybody buying a new camera either. Just replace the film and you were done.
While of course the lens is still a very important part of that equation, for regular shot even comparatively dinky film cameras produce good image quality. The film dictates, to a large degree, how much an image can reasonably be magnified, how grainy the image is, what colour rendering it will have, etc.
Obviously none of this is the case with digital today. The sensor dictates the basic level of image quality and while RAW file allow for some leeway in how the final image turns out, the core quality is what it is and cannot be changed, other than by buying another camera.
Until recently, the sensors used in compact cameras didn't amount to much. They were small and noisy compared to the larger sensors used in DSLRs. Now however,
Olympus and its partners announced the
Micro Four Thirds System (via Photography Blog). This is meant to make compact cameras with near-DSLR image quality and replaceable lenses possible. Like a Sigma DP-1, but not quite. Think Leica CL or better yet: Olympus Pen-F.
Of course these cameras will still be bigger than a current digital compact, like say a Canon SD-series. But they would have the same core features: LCD viewfinders, movie mode, SD or MicroSD flashcards for storage, probably slower autofocus because this needs to be done through image contrast via the sensor, etc.
However, on other fronts these will be a new class of cameras all together. They'll likely have a hotshoe for attaching a flash or an analogue viewfinder as well as other gizmos, and of course the lenses will be replaceable.
To give some idea of how this will look, I've created a quick size comparison between the current Olympus E-420 (the smallest DSLR around AFAIK), a Canon SD790 and a possible Micro Four Thirds camera. For the latter I measured a photograph of an E-420 in photoshop, against its known dimensions. I then removed the part from the top of the camera, to the lens mount, as this is part of the penta-prism construct that will not be present in a Micro Four Thirds camera. Then I halved the thickness as Olympus suggests will be possible for these devices:
(Note that the green Olympus box denotes the size including the viewfinder "bulge". The actual camera is smaller, since that bulge only takes up part of the width of the camera. Sizeasy can only display boxes however.)
As you can see in this (albeit unscientific) comparison, the resulting device has an intriguing form-factor. I would think it likely that the actual device might even be slightly less wide, as I suspect most of the width of the current E-420, beyond the sensor and the SD card is due the need for all the various controls needing a place to be. The control are quite tightly packed already. A µ4/3 camera will likely have less controls to start with (more like a regular digital compact) and as such might be able to squeeze everything into a even tighter package.
Regardless though, this might be kind of camera that will really get a lot of people interested. Not just the semi-pro and pro markets, but also a lot of regular users looking for something better than a pocket digicam, but not willing to go DSLR.
