The diagram below illustrates the relative sizes of the two sensor groups. The cropped DSLR sensor group is shown in orange tones, the compact sensor group in blue tones.
As evident in the diagram, there is a big gap in sizes between the largest compact sensor, the now rarely used 2/3” (8.8 x 6.6mm) sensor, and the smallest DSLR sensor, the 4/3 (18.0 x 13.5mm) sensor. This gap is much larger than the size difference between individual sensors in each of the two groups.
Sigma’s DP1 has used a sensor in the first group of large DSLR sensors. The price of having a very large sensor in a compact body is a not very bright, nor versatile, fixed 28mm lens. All other serious compacts to date (late May 2008) use the much smaller sensors typical in compact cameras. Except for Ricoh’s GRD I/II, all these cameras feature versatile zoom lenses that are at least fairly bright at the beginning of their respective zoom ranges. Because their sensors are small, noise and noise reduction remain an issue in all but the best lighting conditions.
The question is why there isn’t an intermediate size of sensor for serious compacts: a size that fits between the DSLR and compact sensor sizes. These sensors could offer better image quality than those sensors in the compact group while they wouldn’t be so large as to preclude zoom lenses. An intermediate size would be 12.0mm x 9.0mm, which I’ll call the “S/C” sensor. This hypothetical sensor has approximately half the area of the 4/3 sensor and about twice the area of the 2/3” sensor. This sensor should allow for reasonably compact lenses and camera bodies.
Making a sensor for just one class of camera or model seems feasible if we take Panasonic’s LX2/D-LUX 3 as an example. Its unique 16:9, 8.8mm x 4.8mm, was only ever used in that particular camera model. As of May 2008, Fuji’s 2/3” Super CCD HR sensor is also only used in one model: the FinePix S100fs.
So perhaps a new intermediate sensor size could provide a better balance between image quality and a compact form factor.
