As an exercise, I have tested the read noise of my ASI1600MM-Cool. Principles are described by Craig Stark at:
http://www.cloudynights.com/page/articles/cat/column/fishing-for-photons/signal-to-noise-part-3-measuring-your-camera-r1929
First I made a master bias from 50 bias images as a reference. From one bias image this master average was subtracted and a fixed value added to stay positive. The standard deviation of the resulting image pixel values is then read noise level in ADU’s (analog digital units) range 0-64k. This value has then only be converted to electrons, e-.
The values match with the graph is the ASI1600MM-Cool manual. Furthermore you can see that software binning reduces the noise with a factor 2 (SQRT(4)). Less then hardware binning which reduces noise with a factor 4.
The read noise at unity gain and bin x2 is 0.82 e-. Read noise at unity gain bin x1 is 1.67 e-. Noise levels where taken from the center of the image. Some areas where 20% higher. I also measured my QHY8 and it confirms readings published.
The master bias of 50 images is not ideal as a reference since it gives only a noise reduction of SQRT(50), so more should have been included.
Han
Math/calculation:
ASI1600MM-Cool
Bin x 1
Temperature -25 degrees Celsius
Gain is unity gain at 139
Standard deviation:= SD( bias1- average + fixed value) = 26.5 ADU (some areas are 20% higher)
Gain is 5/10^((139/10)/20) => 1.01 (note the gain of the ASI1600 is in 0.1 dB given so the 139 has to first divied by ten to get dB. The power 10 is required to convert the logarithmic scale to linear.)
Extra gain 4k (12 bit) to 64k (16 bit reading) => 16 x
Noise or SD is =26.5*1.01/ 16 => 1.67 electron or e-
All results of my ASI1600MM-Cool:
Gain 300, Bin x 1, -25 degrees Celsius
Standard deviation of one bias image minus the average of 50 bias images: 130 ADU
e-/ADU 0.16
Extra gain 16.00
Read noise or Standard deviation 1.28 electron
Gain 300, Bin x 2, -25 degrees Celsius
Standard deviation of one bias image minus the average of 50 bias images: 65 ADU
e-/ADU 0.16
Extra gain 16.00
Read noise or Standard deviation 0.64 electron
Gain 139, Bin x 1, -25 degrees Celsius
Standard deviation of one bias image minus the average of 50 bias images: 26.5 ADU
e-/ADU 1.01
Extra gain 12 bit naar 16 bit is 2^4=>16 16.00
Read noise or Standard deviation 1.67 electron
Gain 139, Binx2, -25 degrees Celsius
Standard deviation of one bias image minus the average of 50 bias images: 13 ADU
e-/ADU 1.01
Extra gain 16.00
Read noise or Standard deviation 0.82 electron
Gain 0, Binx1, -25 degrees Celsius
Standard deviation of one bias image minus the average of 50 bias images: 12 ADU
e-/ADU 5.00
Extra gain 16.00
Read noise or Standard deviation 3.75 electron
QHY8, Gain 5, 0,375 electron per ADU
Standard deviation of one bias image minus the average of 50 bias images: 30 ADU
ADU/e 2.67
Read noise or Standard deviation 11.25 electron
