Bernd R>Are you sure F setting work really on IXus 300
It is easy to see when you look at iris through lenzes
Also I made shooting test. I've set TV priotity mode in camera menu and set shutter to 1/50, also I set ISO to 800 also in camera menu, so everyghing locked beside aperture. And made shots with different F (set with CHDK) and you can see that images different, so it works. But it's a pity that I can't see this on preview during half press. No matter what I set in this case I always see image like F 2.2 because automatic of camera set this value in this particular case. So aperture override works only for shooting and not for preview.
One note about aperture values in CHDK. Values for aperture that I can set in camera menu
2.0 2.2 2.5 2.8 3.2 3.5 4.0 4.5 5.0 5.6 6.3 7.1 8.0
but in CHDK menu I can set only strange values
2.05 2.31 2.37 2.74 2.95 3.41 3.87 4.23 5.03 5.65 6.34 7.12 8.0
but as I undestood camera make shooting with it normal values - it choose closest to that strange values. But if possible whould be good to make them the same.
>more deeper sharp
Probably you mean DOF (depth of field/focus).
>ND Filter give no deeper sharp, only make all darker
Yes, this is the only purpose of ND - to reduce ammount of light. I measured it for Ixus 980 and found that ND reduce ammount of light in 4 times. Changing aperture from 2.0 to 8.0 probably also make image in 4 times darker (something around that but not sure about exact value). So combination of ND and aperture on this camera can give reduce in light in 16 times, so probably will be possible to shoot sun
. Also ND can help when you focus on something close and whant backgound to be defocused, so you need aperture be maximum opened, but if it very bright and 1/2500 not enought? ND will help here. But in most cases aperture better, because it allow adjust ammount of light very precisely. ND can only reduce it in 4 times and no less and no more.
I can help make any test and tell something about photo, but I am programmer just a little.