I have been experimenting to get a better understanding on how these things work.
Say that I want to take a picture from the cockpit, i.e. behind the glass. It is typically not flat and has scratches or dirt. This gives two problems: dirt is visible on the image and the auto-focus tend to focus on the dirt rather than on the landscape.
The only way I found to get ride of this is to open at F/2 and manually set the focus to infinity. This makes the dirt as far as possible from the DoF and thus less visible. If there is a lot of sun, the minimum integration time of 1/1600 s is yet too long. Using chdk, I override it to say 1/10000 s. The integration time is actually override, but this is a fix setting, so the image rarely has the correct exposure. As the light condition changes a lot in the sky depending on what you are shotting at, it would more useful to shot in aperture priority mode and let the camera adjust the integration time, but with a lower limit down to 1/10000 s or so. Is it possible?
Related question is how the camera adjust the aperture in video mode? Is it possible to force the aperture to f/2, the focus to infinity and the shortest integration below 1/1600 s for the same reason as above?