For 20 years, I have been using charge-coupled device (CCD) cameras, and I currently own the top-of-the-line SBIG STX-16803. But while studying two images I recently made using the latest QHY 410C CMOS camera, I had to wonder: Is CCD dead?
For years, I lectured about the asymptotic boundary of noise in CCD images. In a basic sense, this means that no matter how many frames you take to increase your signal-to-noise ratio for a cleaner image, you will always run into a wall of noise when you stretch your image to bring out deep shadows. But with QHY’s new CMOS camera, this troublesome wall of noise is nonexistent.
The QHY 410C is a one-shot color camera that utilizes the back-illuminated Sony IMX410 CMOS chip found in high-end cameras like the Nikon Z6 and the Sony A7 III. But the 410C has taken the full-frame (35 millimeter) 24-megapixel chip and mounted it in a camera with regulated cooling and zero amplifier glow, helping drive the noise to such a low level.
There also aren’t any noticeable cosmic ray hits, despite high quantum efficiency. (Quantum efficiency is the percentage of photons that are converted into recorded data.) With my SBIG STX-16803 CCD, quantum efficiency is around 60 percent; with a back-illuminated CMOS, it’s about 80 percent.
The commercial availability of these back-illuminated chips has been a big game-changer in photography. In a normal, front-illuminated chip, all the supporting electronics surround each light receptor (pixel). Thus, some of the area that receives light does not record it. In a back-illuminated chip, the supporting electronics are on the back of the chip, allowing 100 percent of the light receptors to absorb and record light. This results in a chip with much higher sensitivity, which is ideal for astronomy and astrophotography.