The breakthrough Sigma SD9 camera with Foveon technology has the world's first image-sensor that features three layers of photodetectors. The layers are embedded in silicon to take advantage of the fact that red, green and blue light penetrate silicon to different depths allowing full-color to be measured at every pixel. The layers are positioned to take advantage of the fact that silicon absorbs different colors of light at different depths, so one layer records red, another layer records green and the other layer records blue. This means that for every pixel on a Foveon X3 image sensor, there's actually a stack of three photodetectors, forming the first and only full-color capture system.
Dust and dirt entering through the lens mount of a digital camera, can create serious defects in image quality. If dust and dirt adhere to the image sensor and are not removed, it will deteriorate the image quality. In order to prevent dust entering and adhering to image sensor, the body mount of SIGMA SD9 is equipped with an integral dust protector. The dust protector of the SIGMA SD9 prevents dust from entering and adhering to the image sensor. Even if dust adheres to the dust protector it will not have an influence on image quality because the dust protector is located away from the image sensor.