I have the Canon SD800 IS camera with firmware 1.00D and I am using CHDK build #51-444. I have elected to name my RAW files using CR2. The pdf manual for CHDK is now out-of-date for this build because several screens have changed.
As you have described above, and I have experienced, Custom Auto ISO really doesn't work at all in the SD800 IS camera.
Unfortunately, this build takes away the ability to override AV [aperture] settings and instead offers ND filter state OFF, IN or OUT. The Canon SD800 IS supports variable apertures [e.g. 2.8, 3.5, 4.0, 4.5, 5.0, 5.8], so it is not as simple as selecting the ND filter IN or OUT. In Build #50, you could select an override for aperture, but I don't know if it really works.
In addition, with this latest build #51-444, overriding ISO doesn't work either for Bracketing or at the higher level directly in Extra Photo Operations.
The biggest deficiency that I have discovered with CHDK with the Canon SD800 IS, like you mentioned above, is that after you have taken a photo and you flip to Display to review your image with detailed shooting information, you don't see the settings for ISO, TV or AV that were used to generate the image. Of course, I can use a program [e.g. BreezeBrowser] external to the camera to display the *.DNG file and see the EXIF metadata, but you really need to see this data in the camera, as you can with a DSLR [e.g. Canon EOS 40D].
I have also discovered that at least seven EXIF data items, which exist in the original JPG file, do not get transferred when you Convert to a DNG file. Although this is not the most important data which is missing, there is really no reason for it to be missing.
When using bracketing, I have discovered that under certain circumstances, the ISO will not be shown in the DNG file when viewed in external software. I suspect that this is a size of number issue and once the ISO exceeds say 500, it won't display.
I was quite surprised to discover that CR2 files, right out of the SD800 IS camera, can be read by BreezeBrowser software but not by Photoshop CS3. Even if Photoshop could read the file, you should still Convert to DNG files because this is how you port the EXIF data from the JPG file to the raw file [DNG].
If you are using bracketing and doing it based on ISO [once it is working properly], another input parameter is required so that you can specify at what increment the ISO is increased or decreased as you shot in continuous mode.
In Extra Photo Operations, I discovered that if you set Override shutter speed to 1/250 and the corresponding Value factor to Off, and you then set Override ISO value to say 15 and the ISO Value factor to 10, the resulting ISO override will be 250 and not 150 when you take a photo with these settings.
Here is another major deficiency: If you delete an image from within the camera, it will do the usual and delete the JPG file, but it won't deleted the CR2 raw file for that same image.
I hope that my hours of testing and this review regarding CHDK has provided constructive criticism to make CHDK eventually into a viable , trusting and powerful enhancement to Canon P&S cameras.
Regards,
Gary