Even if I still didn't find a solution to get better low light sensibility, in order to have night images, I made a 3 days test with a different lens :

which promises to have better aperture. It's an adruCam module, the overall quality is good for the price you can it get from ebay.

I face two problem. The first one is visible on the small Gif animation on the top of this log. The Sun, in all its glory, leave a mark on the CCD sensor ! Well, the sensor or the filter on the top.

Second problem is related to the sun as well. When it appear in the field of view of the camera, the image is blurry and the right side is out of focus. I presume the non-uniform heat deposition on the focus plane makes physical deformation...

Well, not an easy game there. I have to continue investigations on an hardware solution.