Reply To: Starting CMOS photometry

Forums Photometry Starting CMOS photometry Reply To: Starting CMOS photometry

Dr Paul Leyland

Thanks Ian,
Very useful starting point for me.
Some imagers have advised to cool to only zero, but I believe that there is some advantage in going cooler with CMOS cameras, but I’m not sure about this.

You should cool to the point where the thermal noise is negligible compared with other sources of noise, such as sky background, Poisson noise, and so on.

Where that point lies depends strongly on the camera and, to some extent, on the sky background. For my present camera (a SX-814 CCD) -10C is easily cold enough and well within the reach of its Peltier cooler except in the very hottest of summer nights. Air temperatures of 25C are not unknown in La Palma and were reached this last summer on a few nights, but they are not common.

It’s easy enough to measure the thermal noise of your camera as a function of temperature. Take some (say) 60 second darks at a variety of temperatures and look at the variance of the pixel values.