Amplifier Glow in CCD / CMOS Cameras

Amplifier glow refers to a glow you would get in an image that is primarily caused by the imaging camera.  We usually refer to it as Amp Glow and it is generally caused by the heat from the readout circuitry of the imaging chip.  For CCD cameras, it was generally caused by the amplifier that, with the rest of the chip’s circuitry was located on the chip frame.

We now generally use Complimentary Metal Oxide Semiconductors (CMOS) cameras such as the QHY 294M that I use in my backyard.  The circuitry in these particular cameras is integrated with the pixels on the sensor.  Each pixel has the Analog to Digital Converter (ADC), clock generators and other general circuitry integrated with it.  The circuitry can generate heat in the Near Infrared light and can cause glows on your image.  You see this most often in dark frames such as the one I’ve attached.  As a general rule, the longer the exposure time, the brighter the Amp Glow seems to get and this will definitely be a problem when you process your light frames.

The general recommendations I’ve found to deal with this problem are:

(1)  Amp Glow is generally removed by subtracting a properly constructed master dark frame.  To create a solid master dark, make sure you capture your dark frame sub exposures  (generally 20 to 30) at the same temperature, exposure time, gain and offset settings as you did your light frames.

(2)  When you calibrate your light frames, use the master dark frame, master flat frame and master dark flat frame.  Apparently a master bias frame will not help and it’s not recommended to be used.

(3)  If your calibration software has a dark optimization feature, disable it.  If this feature is enabled during calibration it will scale the master dark and could result in a mismatch with any glows in the light frame, possibly making the problem much worse.