- For me, the aperture settings of a camera are related to hardware limits (optics). How can CHDK extend it?
- The same for faster shutter speed. The curtains have a intrinsic inertial limit. How can CHDK extend it?
CHDK can't make the aperture wider. CHDK can make it more narrow than Canon has chosen to allow in their firmware because the hardware can do that. The reason Canon doesn't allow those narrowest apertures is probably because it deteriorates image quality due to tiny mechanical dimensions and because usually you'd just get unacceptable noise performance trying to use those apertures.
As for shutter speed, there are no curtains. The shutter in P&S cameras is electronic (part of the sensor), and it can work a lot faster than shutters you generally find in DSLR cameras. There is a mechanical shutter, but it's just for covering the sensor during photo readout, not for timing the exposure so it's speed is not an issue. Again, Canon doesn't let you choose very fast shutter speeds, probably because they aren't required by most users, because they'd make DSLR's look bad and the same light requirement/noise thing as you get with narrow apertures. Note that while CHDK may attempt to set reidiculously fast shutter speeds, it doesn't always mean the camera is really physically able to do that.
