This may bring a different slant on amp glow with the ZWO ASI 1600MM/C cameras.
I bought a ZWO ASI 1600MC in August last year.....i.e. winter here in Australia. Initially I had no problems, but as time wore on I started seeing amp glow, which by now is quite severe and limiting what I can produce from the camera. It is now summer here in Australia and at night time the temperature can be upwards of 20C (68F). After some investigation I believe the ambient temperature is the source of the issue. To test this out I ran 40 darks with the camera in the fridge at 6C (43F)......the stacked dark had no observable amp glow and a mean ADU of 1.2. After performing the same test at room temperature 22C (72F) there is very noticeable amp glow, particularly in the top and bottom right hand corners of the image and the mean ADU was 5.1. In both cases the gain was set to 150, the exposure time to 2 minutes and the set temperature to -20C (-4F), which was being achieved according to the probe readout. Theoretically the ambient temperature should make no difference to the darks so produced.
Here is a DropBox Link to stretch images of the two Master Darks side by side. The left hand image is the fridge test.
So why the difference? At 6C (43F) the power consumption was only about 15%-20% and the body of the camera when I removed it from the fridge is mildly warm to touch. At 20C (68F) the power consumption was nearly 100% and the body of the camera when I picked it up is really hot to touch. I estimate it to have been at least 50C (122F). The cooling fan was working in case you are wondering.
It is my belief that the design of the camera (or some vagary of my version of it) is such that at warm ambient temperatures, with the solid state refrigeration system working hard to reject the heat from the sensor, the heat so produced is not being adequately removed from the body of the camera to be extracted with the cooling air. As a result the temperature of the body of the camera rises. It rises to the point where the temperature difference is great enough to force the heat to be rejected. However this means the camera gets very hot. It is more than likely that this high temperature leads some heat to be transferred by conduction to the periphery of the sensor where it manifests itself as increased dark current noise i.e. amp glow.
One major problem with this amp glow is it cannot be easily removed by dark subtraction. The first reason is that the amount of amp glow depends on the ambient temperature at with your lights and darks are taken. These may not be the same. Secondly there is a time dependency. When the camera is first started up it is at ambient temperature. It heats up over time, so the amount of amp glow is changing over time, such that you cannot reliably take a set of darks and know they pertain to the lights you are taking at another time.
For example here is a single debayered sub from my recent imaging of Thor's Helmet. The amp glow is visible to the upper and lower right of the image as a blue-white glow.
Here is the same sub after calibration by dark subtraction only.
These darks were taken immediately after the lights, bias and flat frames. By then, it is my belief, the camera was hotter than when the lights were produced and the amp glow worse. When I did the dark subtraction the extra blue from the extra amp glow was subtracted leaving a green/ red periphery. It looks green so how do I know there is red there. When I used the SCNR routine in PixInsight to subtract green chrominance noise to try and get rid of the glow, it turns red.
Perhaps where owners of this camera have seen the amp glow get fixed or suddenly get worse, it's because the ambient temperature has changed.
Edited by macnenia, 19 February 2018 - 06:44 PM.