Sigma follows up its must-have new lens announcements with a who-wants-it? debut of its first mirrorless interchangeable-lens cameras, the Sigma sd Quattro and sd Quattro H. Sigma didn't release a lot of specs for the cameras (though B&H seems to have them), so it's possible there's some buried treasure in there somewhere. But aside from the Foveon sensor and the Sigma lens mount, there doesn't seem to be anything novel or noteworthy about them. And as yet there's no price for them, and that will factor heavily in just how much even those will matter. Sigma hasn't revealed an expected ship date, either.
The two cameras differ by the sensor. The sd Quattro uses the same APS-C sensor as the Sigma dp2 Quattro line, while the sd Quattro H uses the same sensor technology in the larger APS-H format, which has a focal-length equivalent of 1.3x of full frame, about the same size as the 1.5-inch sensor Canon uses in its G1 X series.
The Foveon X3 sensor is composed of red-, green- and blue-sensitive layers; the top blue-sensitive layer has four times the number of photodiodes as the red and green channels. It uses those to create a luminance channel (that's the image detail), which is then combined with the color data to form the full-color picture. Sigma math -- in which the company defines a "pixel" as a single color element rather than an actual picture element -- takes the 19.6-megapixel sd Quattro and 25.5MP sd Quattro H sensors and claims they're equivalent to 39MP and 51MP Bayer-array sensors, respectively.
As always with the Foveon sensors, my belief is that they might deliver better color and detail than other sensors with similar numbers of pixels, but the spatial resolution of the final files is represented by the lower numbers. Sigma includes a new Super-Fine Detail mode that's really in-camera HDR, but unlike other cameras it merges seven exposures together rather than two or three.
The magnesium-alloy body is dust- and splashproof, which is nice, and it has an electronic viewfinder, but otherwise the specs are kind of ho-hum. It's fairly large and heavy -- close to the size and weight of a midrange dSLR like the Canon EOS 70D. And it doesn't support video, lacks Wi-Fi connectivity and built-in flash, and has rated continuous-shooting speeds of just under 4 frames per second (and it's not clear if that's with or without autofocus).
Though it's oddly designed, with the sensor section much bigger than the grip, it actually looks fairly comfortable to hold. But overall, unless all you care about is the sensor, they don't seem very compelling; and if the sensor matters that much to you, the sd Quattro H looks like a more attractive option.