Anyway, can anyone tell me the best settings for nightlapse or taking pictures of the stars at night?
Some general tips:
* Use a tripod. For an ixus, the little $5 mini pods you can find on amazon etc are fine.
* Use a script with an initial delay or the USB remote, so that triggering the shutter doesn't shake the camera.
* Exposure as long as it can be without star trails bothering you too much, up to a few minutes. For a wide shot, 15 - 30 seconds is probably a reasonable starting point. If you want really extreme star trails, you probably want to take multiple exposure stack them with software (either "lighten" in gimp/photoshop, or a dedicated program like starstax or startrails)
* ISO as high as you can go without the noise bothering you too much. On an old camera like IXUS 80, probably 400 or less.
* IXUS 80 doesn't have a an adjustable aperture, but wider zoom will gives a larger effective aperture.
* The camera will probably have trouble focusing on stars. IXUS 80 doesn't have manual focus, but you should be able to use CHDK override. Using infinity is probably good enough, but check before you take a bunch shots.
* You can get more out of your shots using DNG (raw) but processing them requires a learning curve. You will need to use a proper raw processing program like raw therapee, darktable, etc.
* Shooting raw also causes delay of a few seconds between shots, which isn't good for trails.
* Normally, the Canon firmware does "dark frame subtraction" (DFS) for exposures longer than about a second. This means the camera takes a second shot with the shutter closed for noise reduction, which helps quality significantly but means your shots take twice as long.
* CHDK lets you turn DFS off, but you will see more hot pixels and "amp glow" without it. You can get the best of both worlds by taking dark frames separately and subtracting them after the fact. This works best with raw. Creating the separate dark frames can be done with the script waterwingz suggested or the one I linked below.
* If you want really "deep" images, you need more exposure than you can get before the stars start to trail. The best way is a telescope mount that tracks the rotation of the earth, but they are expensive. It's also possible to take multiple images and align them using software like deep sky stacker.
The script I use for this kind of thing is
http://chdk.wikia.com/wiki/Lua/Scripts:_Fixed_Exposure_Intervalometer There are some examples with settings on that page. It's pretty similar to the one waterwingz suggested.
