My understanding of lightning shots is that one would need to take multiple shots quickly after the up-bolt to ensure you get the "perfect" shot of the lightning bolt.
the problem is your camera is powershot digital camera.
it is not special cam which can make shoots every 10(50) msecs....
- amount of RAM available
- time required to make shoot
- time to be ready to make next shoot
- SD card write speed
I did no measurements to check what is minimal interval between shoots is but I'm sure you can make only one shoot of the same lightning bolt.
to make several shoots without storing them to SD card camera must have either alot of RAM available or very quick writing speed to memory storage device (SD card)
You cant make several shoots of the same bolt.
I would be happy if i'm wrong
This said, I don't see a way to put the camera into continuous hi-speed drive while still in motion detection mode. Could anyone advise me how I could do this?
motion detection feature do not depend on mode you have selected.
You can make any count of shoots as you like (using either CHDK or original fetures).
I'm not a photographer.
I would suggest you to make several shoots in most quick mode (no lightning).
analising exif data you could calculate time difference between shoots.
if it is small enough to capture the same bolt twice - good for you ( but I don't beleive it)