I don't think that camera of n900 has any aperture (except for the aperture of lens - f/2.8) - only way to control exposition is therefore changing shutter speed and iso... and i'm not completely sure ISO changing is hardware-supported either (i.e. whether it isn't simulated by simply multiplying pixel values)..

dunno about the focusing - I've thought the video app has to control this, but seeing the focus_auto option makes me wonder........

there's a "mirror" app in repos - a simple python script showing how to handle v4l devices using python.. let's try hacking it to play with the back camera..