Another observation. In my camera I used AD811 opamp from China (ebay). Based on price (US$2.99) and how it looks, I am quite sure it is not a genuine part.
Today I tried another opamp that I had lying around, THS4031 that came from Farnell few years ago and is for sure genuine. Comparing bias frames between the two, and without sensor, standard deviation for AD811 is 19ADU, and for THS4031 is 10ADU. That is clear and massive improvement.
I was in a hurry doing the tests, so for now take this with a grain of salt.
Those two opamps should be comparable in performance, with slightly lower noise on THS part. But who knows what is really encapsulated in a AD package...
More tests will follow
