Spectral color

Astronomy tests the QHY 410C, a noise-free color camera

I have been using Charge Coupled Device (CCD) cameras for 20 years and currently own the high end SBIG STX-16803. But studying two images I recently took with the latest QHY 410C CMOS camera, I wondered: is the CCD dead?

For years I have lectured on the asymptotic noise boundary 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 sharper image, you will always hit a wall of noise as you stretch your image to bring out the shadows. deep. But with QHY’s new CMOS camera, that annoying wall of noise is non-existent.

The QHY 410C is a single-shot color camera that uses the Sony IMX410 back-illuminated CMOS chip found in high-end cameras like the Nikon Z6 and Sony A7 III. But the 410C took the full-frame (35-millimeter) 24-megapixel chip and mounted it in a camera with regulated cooling and zero amplifier glow, helping to reduce noise to such a low level.

There are also no perceptible cosmic rays, despite high quantum efficiency. (Quantum efficiency is the percentage of photons that are converted into recorded data.) With my SBIG STX-16803 CCD, the quantum efficiency is about 60%; with a back-illuminated CMOS, it’s about 80%.

The commercial availability of these back-illuminated chips has changed the game in photography. In a normal front-lit chip, all of the supporting electronics surround each light receiver (pixel). Thus, part of the area that receives the light does not register it. In a back-illuminated chip, the supporting electronics are at the back of the chip, allowing 100% of the light receptors to absorb and register the light. This results in a chip with much higher sensitivity, ideal for astronomy and astrophotography.