Sigma's analogues are loved by photographers for their serious image quality and relatively low prices compared to the original factory, and Sigma's cameras are undoubtedly extremely niche products, but niche does not mean backward, on the contrary, Sigma produces the most unique cameras.
 
There is only one reason to buy a Sigma camera: it is comparable to the image quality of a medium format camera.
 
The image sensors in our common mobile phones and cameras use a "mosaic" structure, where each pixel is composed of three primary color sub-pixels arranged in parallel with a smaller area, and the sub-pixels each record brightness information, and finally restore the color through superposition calculations. The Foveon X3 sensor arranges the three primary color sub-pixels vertically according to the wavelength of light, which is closer to the principle of film, and each pixel records complete color and light and dark information, and the resulting image naturally has the grainy texture of film. In good light, the APS-C format Foveon X3 sensor can match even the color and resolution of commercial medium format cameras, and a single photo will generate hundreds of megabytes of data, which is higher than that of the medium format Hasselblad X1D.
 
However, this sensor also has many flaws, the biggest problem is that the power consumption and heat generation are much higher than those of conventional sensors. As a result, the Sigma camera is easy to overheat and limit its use after it is turned on, and the battery life has also been criticized, which requires more than one backup battery. Second, the three-layer sensor makes the bottom layer less receptive to light, and although the Sigma camera can reach up to 6400 IOS, it actually starts to show noticeable noise and color casts beyond ISO-400.
 
Sigma has released two mirrorless cameras with the Foveon X3 sensor, namely the SD Quattro in APS-C format and the SD Quattro H in APS-H format, the latter has 59 million pixels, which is the highest resolution mirrorless camera available, and the price is less than 10,000 yuan. However, these two cameras are not unpopular for no reason, and it is not recommended to buy these two cameras for the sake of image quality. In addition to the obvious flaws mentioned above, these two cameras use the Sigma SA mount, which is a DSLR mount that has been abandoned, so both models do not have the thinness and lightness that mirrorless cameras should have, and the SA lens group is also extremely niche and has not been updated for a long time. If you like the excellent image quality brought by the Foveon X3 sensor, you can choose Sigma's high-end card machine DP-Quattro, which has the same specification sensor, without the trouble of lens groups, and the body is more compact and convenient.
 
Even more exciting is Sigma's future full-frame camera. In the fall of 2018, Sigma announced that it had formed an L-mount alliance with Leica and Panasonic to develop full-frame mirrorless cameras. The advantage of the alliance is that there is no need to worry about the lens, and the weak electronic performance of the Sigma camera is expected to be compensated, and the image level of the APS-C format Foveon X3 sensor is already comparable to that of medium format, and the new product with the full-frame Foveon X3 sensor is definitely worth looking forward to.

SIGMA/Sigma sd Quattro mirrorless camera (APS-C mirrorless camera) ¥6388.00