Sigma's mirrorless Foveon body — the SD Quattro, X3 Quattro sensor, SA mount, EVF, no video, 2016.
The Sigma SD Quattro is a mirrorless camera announced in 2016, part of Sigma's SA-mount line and built around the Foveon X3 Quattro direct image sensor. It broke from the earlier reflex SD bodies by adopting a mirrorless design with an electronic viewfinder while keeping the Sigma SA mount, continuing the Foveon approach in a new form.
It is a mirrorless camera with no reflex mirror, using an electronic viewfinder and the Sigma SA bayonet mount for Sigma SA lenses. Its APS-C-class Foveon X3 Quattro sensor uses three stacked layers with a revised distribution of resolution between them, capturing colour at each location rather than interpolating it. The body has no in-body stabilisation, records raw for Sigma Photo Pro, offers no meaningful video, and uses SD-type media in a weather-resistant shell.
The SD Quattro suits landscape, portrait and studio photographers who want the Foveon rendering with the framing benefits of an electronic finder that previews exposure. It performs best at low ISO and works deliberately, so it favours considered, tripod-based shooting over fast action, in keeping with the character of the Foveon line.
When buying used, expect slow operation and heavier battery drain than Bayer mirrorless bodies, so test power and carry spares. Check the shutter count where readable, inspect the exposed sensor for dust, and test the EVF and rear screen for dead pixels. Confirm the card and battery doors and weather seals, check the SA mount for wear, and note that raw processing relies on Sigma Photo Pro with limited service support for the line.