Sigma’s DSLRs feature the unique Foveon image sensor, which unlike conventional image sensors, records all three primary colors at every pixel site, potentially resulting in better image quality. The main drawback has been that these cameras have had a relatively limited number of pixel sites—the current sensor contains 14 million pixels, but stacked in three layers, so it produces images measuring 2640x1760 pixels.
That appears to be changing with the recently announced Sigma SD1, which contains a new Foveon sensor with 46 million pixels and 15.3 million photosites—just below our arbitrary 16-megapixel “line” for this article, but certainly competitive with any of the cameras cited here in terms of ultimate image quality potential.
Four Thirds Cameras
The Four Thirds System comprises a line of compact DSLR bodies based around (and designed specifically for) a smaller 17.3x13.0mm Four Thirds image sensor. The smaller sensor allows for smaller camera bodies, smaller lenses and a more direct path of the light to the image sensor, providing the potential for better image quality for a given pixel count. Curiously, though, most Four Thirds System DSLRs aren’t all that much smaller than APS-C format DSLRs.
More recently, Panasonic introduced the Micro Four Thirds System, based around the same 17.3x13.0mm sensor size, but replacing the bulky (and costly) SLR mirror box, moving mirror, focusing screen and pentaprism or pentamirror optical finder with full-time Live View and (in some models) an eye-level electronic viewfinder. These mirrorless cameras have fulfilled the original Four Thirds System promise of truly smaller cameras. If you don’t care to lug bulky gear around on your outdoor excursions, Micro Four Thirds provides an attractive alternative to larger formats. Panasonic’s Lumix DMC-GH2 features 16.05 megapixels, and thus meets the pixel-count criteria of this article even though it isn’t actually a DSLR. (Note: Samsung and Sony now offer mirrorless interchangeable-lens cameras with APS-C sensors and the compact size of the Micro Four Thirds models.)