Sigma's Foveon DSLR — the SD15, X3 layered sensor, SA mount, OVF, no video, 2010.
The Sigma SD15 is a digital SLR announced in 2010, part of Sigma's SA-mount SD line and built around the Foveon X3 direct image sensor. It followed the SD14 in the series and continued Sigma's use of the layered Foveon design instead of a conventional Bayer array, aimed at photographers who valued that sensor's particular rendering.
It is a digital SLR with an optical viewfinder and a moving reflex mirror, using the Sigma SA bayonet mount for Sigma SA lenses. Its Foveon X3 sensor records red, green and blue at each location through three stacked layers rather than interpolating colour. The APS-C-class body records raw files processed in Sigma Photo Pro, has no in-body stabilisation, and offers no meaningful video. It uses SD-type media and improved on earlier SD bodies with a larger rear screen.
The SD15 suits photographers who want the distinctive Foveon look for landscape, portrait and studio work at low ISO, prizing per-pixel detail and colour character over speed. Like other Foveon SD bodies it is best used deliberately, with modest high-ISO latitude, and it rewards careful exposure and a tripod-based approach.
On the used market, expect slow operation and quicker battery drain than Bayer DSLRs, so test power and carry spares. Check the shutter count where readable, inspect the sensor for dust and the finder and screen for haze or dead pixels, and confirm the card and battery doors latch. Raw output relies on Sigma Photo Pro; service for the Foveon line is limited, so buy a tested example and plan the workflow around it.