The difference between the two cameras is with the sensor size. The sd Quattro H uses a large APS-H sensor (30 percent larger than an APS-C sensor) that, according to Sigma, shoots photos equivalent to a 51-megapixel DSLR with a Bayer-pattern sensor. The Foveon sensor uses a stacked-layer design: The top 25.5-megapixel silicon layer captures all detail information as well as color information for the blue channel, while two five-megapixel layers beneath handle red and green colors. There’s no need for a low-pass filter, and Sigma says the image quality is comparable to medium-format files.
The sd Quattro uses an APS-C sensor (also in the dp Quattro compact camera series) that produces images equivalent to a 39-megapixel Bayer-pattern sensor, with a 19.6-megapixel top layer. Both models use a Dual True III image processor and an enhanced hybrid autofocusing system (phase detection for speed, and contrast detection for accuracy), and are capable of shooting RAW.
Other than the sensor, both cameras share the same magnesium alloy body that’s dust- and splash-proof. A 2.3-megapixel electronic viewfinder in built in, with 100-percent field-of-view.
Sigma hasn’t revealed full specs and other details, including pricing and availability. Based on B&H’s spec sheet, it looks like the cameras won’t do video, so we imagine Sigma is targeting still photographers who want great image quality from an ILC without going to full-frame. We will update this page when new information from Sigma is revealed.