[The_bluester (Paul)]

I would say that they are all "Regulated" even older cameras show that, it is just a matter of how tightly they are regulated. All the cooled cameras I have seen look to me to be temperature regulated by a PID system, the bigger the difference from the setpoint, the bigger the steps in cooling power each time and then the last little bit takes longer as it takes time to integrate the smaller error to drive a correction signal.

I would expect the cooling versus power to be non linear, at my guess the peltier coolers will be driven by a PWM signal and the cooling power percentage will be the PWM duty cycle, from there it is just like your aircon at home, the amount of cooling power increase required per extra degree of temperature delta from ambient increases degree by degree.