Normally on a camera; point or shoot or DSLR, using the Auto ISO is a bit of a risk as it has quite a high range and noise might become an issue to your image quality.
The Auto ISO on the G9 limits the ISO to a max of ISO 200 so the image quality is kept, even when cranking the aperture down to f8.0 in Av mode and it still stops at ISO 200 and if light is in the plenty, the Auto ISO will drop all the way back down to ISO 80.
So in short if you want to keep the images at high quality but are in changing light conditions switch it to Auto ISO
A really good tip on how to use your canon G9 at night by Derrick Story
When I’m in big cities, I try to travel by foot as much as possible. That’s when I see the good shots, and if I’m lucky, I come home with one or two.
I was walking back from a dinner meeting in Las Vegas with a Canon G9 and a small Gorillapod tucked away in my jacket pocket. I felt like shooting something, but nothing caught my eye until I climbed a set of stairs for a street overpass and noticed this scene. I wanted the streaming lights of traffic driving by, but I thought they would look best in context with the Las Vegas cityscape.
I mounted the Canon G9 to the Gorillapod and wrapped its legs around the edge of the overpass so I could compose the scene. I made sure the flash was turned off and set the ISO to 80 to control noise. I then went to manual exposure mode, which is very easy to use on the G9, and played with the settings until I saw what I liked on the LCD screen. The exposure was 1.3 seconds at f-2.8. I set the self-timer to anticipate when traffic would begin to move, then pressed the shutter button.
Some of the frames didn’t have the right look. But this image has a nice combination of moving lights and stationary objects. So it became my “keeper” for the night.
Photo of Las Vegas traffic by Derrick Story using Canon G9, 1.3 seconds at f-2.8, ISO 80, using manual exposure mode.
The Digital Story: “How I Did It” 3 – Las Vegas Night Traffic