Sensor type question

Why does the DECam use CCDs and not the apparently better CMOS sensors?

Aren’t cmos just cropped sensors anyways?

CCDs are more sensitive. 100% of the silicon area is active, without any funny business with micro-lenses. Also, they’re WAY easier to calibrate, because there are only a small number of amplifiers, while every pixel in a CMOS is its own amplifier.