I made some progress on getting more sensible setting from the automatic gain control (AGC) of the raspberry camera module, especially for night time pictures.

With the help of 6by9 I modified a bit the Raspistill program. Actually I use it through a Java program which receive the images on stdout. As far as I understood, there is at least 3 component used on the camera system. One is the preview port, another the video, and the Still port. The AGC use the preview port, and it can be configured on one of the two available frame rate modes. The modes are: 0.166 FPS to 1 FPS (6sec exposure time to 1sec exposure time) and the other is from 1 FPS to something like 30 FPS. In the raspistill code we can force one of the mode, the longer exposure time, to let the AGC calculate more sensible parameters.

Raspberry pi forum

And it works, I can have pictures with around 3 seconds exposure time, at 400 iso. I tested with the raspiVid program as well. Force slow FPS mode, and RGB uncompressed data to stdout.

For the moment, I found that the images from the video port are somehow brighter but less precise. At the opposite Still port is still darker, but much better on daytime.

On the left side: stacking and leveling with RGB data from RaspiStill (raspiyuv), and on the right side: stacking and leveling with RGB data from RaspiVidYUV.

To conclude shortly, I think I should consider change the lens of the camera. The small original lens is 'only' f3.5 and there is f2.0 or even f1.4 lens available. Lets search a bit on ebay and make other trials.