Exposure is 315s at 704 gain for the first series of shots. Amplifier glow is very significant at upper left corner, noise is everywhere when uncooled. Camera runs for 10 minutes uncooled before experiment:
First two are uncooled, noise is very serious, I doubt whether it's useable at all.
Peltier cooler turned on, notice that the noise level soon becomes something like the average of the first two shots:-
So now we show only half of the otherwise consecutive darks frames, i.e. we skip one for every two consecutive frames:-
Noise is reduced gradually along as the temperature drops. The dark frame is pretty noise even up to the 9th frames, so I lowered gain to 400 afterward, see if there's any improvement:
The improvement is encouraging and immediate, similar to the zero gain dark frames which I got before, after just two frames (~10 minutes), so I pushed up the gain to 548 to see how worse it would become:
It's not very good, I would conclude that gain of around 400-450 is maximum to be used for long exposure like 5 minutes.
So, finally, I turned gain down to 400 again but push the exposure to 531s (around 8.85 minutes) for some more frames:-
You see, pushing up exposure is not as worse as turning up the gain, the amplifier seems to be a main contributor to the noise, and from the temperature of the heat sink, I feel that if I push the gain high, it will make them heat sink far warmer. By pushing the exposure time, however, the noise level remains very respectable since the camera stays cooler in that case.